Re: Changing strings in files

[Mike Dewhirst]

On 10/11/2020 5:24 pm, Manfred Lotz wrote:

I have a situation where in a directory tree I want to change a certain
string in all files where that string occurs.

My idea was to do

- os.scandir and for each file
- check if a file is a text file
- if it is not a text file skip that file
- change the string as often as it occurs in that file


What is the best way to check if a file is a text file? In a script I
could use the `file` command which is not ideal as I have to grep the
result. In Perl I could do  -T file.

How to do best in Python?
Not necessarily best but I rolled this earlier. Much earlier. But I 
still use it. I don't need to worry about text files or binary because I 
specify .py files.


 


# -*- coding: utf-8 -*-
"""
Look for string 'find' and replace it with string 'repl' in all files in the
current directory and all sub-dirs.

If anything untoward happens, laboriously retrieve each original file from each
individual backup made by suffixing ~ to the filename.

If everything went well, make find == repl and run again to remove backups.

"""
import os

find = """# Copyright (c) 2019 Xyz Pty Ltd"""

repl = """# Copyright (c) 2020 Xyz Pty Ltd"""

ii = 0
kk = 0
for dirpath, dirnames, filenames in os.walk(".", topdown=True):
if "migrations" in dirpath:
continue
for filename in filenames:
if filename.endswith(".py"):  # or filename.endswith(".txt"):
fil = os.path.join(dirpath, filename)
bak = "{0}~".format(fil)
if find == repl:
if os.path.isfile(bak):
ii += 1
os.remove(bak)
else:
with open(fil, "r") as src:
lines = src.readlines()
# make a backup file
with open(bak, "w", encoding="utf-8") as dst:
for line in lines:
dst.write(line)
with open(bak, "r") as src:
lines = src.readlines()
# re-write the original src
with open(fil, "w", encoding="utf-8") as dst:
kk += 1
for line in lines:
dst.write(line.replace(find, repl))
print("\nbak deletions = %s, tried = %s\n" % (ii, kk))


 






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Re: Changing strings in files

[Chris Green]

Loris Bennett  wrote:
> Having said that, I would be interested to know what the most compact
> way of doing the same thing in Python might be.
> 
Here's my Python replace script:-


#!/usr/bin/python3
#
#
# String replacement utility
#
import os
import re
import sys
import shutil

def replaceString(s1, s2, fn):
tmpfn = "/tmp/replace.tmp"
tofn = fn
#
#
# copy the file to /tmp
#
shutil.copy(fn, tmpfn);
#
#
# Open the files
#
fromfd = open(tmpfn, 'r');
tofd = open(tofn, 'w');
#
#
# copy the file back where it came from, replacing the string on the way
for ln in fromfd:
ln = re.sub(s1, s2, ln)
tofd.write(ln)
tofd.close()

s1 = sys.argv[1]
s2 = sys.argv[2]

for fn in sys.argv[3:]:
if (os.path.isfile(fn)):
replaceString(s1, s2, fn)
else:
for srcPath, srcDirs, srcFiles in os.walk(fn):
for f in srcFiles:
replaceString(s1, s2, os.path.join(srcPath, f))

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Re: Changing strings in files

[Manfred Lotz]

On Tue, 10 Nov 2020 08:19:55 +0100
"Loris Bennett"  wrote:

> Manfred Lotz  writes:
> 
> > I have a situation where in a directory tree I want to change a
> > certain string in all files where that string occurs.
> >
> > My idea was to do
> >
> > - os.scandir and for each file
> >- check if a file is a text file
> >- if it is not a text file skip that file
> >- change the string as often as it occurs in that file
> >
> >
> > What is the best way to check if a file is a text file? In a script
> > I could use the `file` command which is not ideal as I have to grep
> > the result. In Perl I could do  -T file.
> >
> > How to do best in Python?  
> 
> If you are on Linux and more interested in the result than the
> programming exercise, I would suggest the following non-Python
> solution:
> 
>find . -type -f -exec sed -i 's/foo/bar/g' {} \;
> 

My existing script in Perl which I wanted to migrate to Python I used 
 `-T $file` and called sed

I like the -T which I assume does some heuristics to tell me if a file
is a text file. 

-- 
Manfred



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Re: Changing strings in files

[Loris Bennett]

Manfred Lotz  writes:

> On Tue, 10 Nov 2020 08:19:55 +0100
> "Loris Bennett"  wrote:
>
>> Manfred Lotz  writes:
>> 
>> > I have a situation where in a directory tree I want to change a
>> > certain string in all files where that string occurs.
>> >
>> > My idea was to do
>> >
>> > - os.scandir and for each file
>> >- check if a file is a text file
>> >- if it is not a text file skip that file
>> >- change the string as often as it occurs in that file
>> >
>> >
>> > What is the best way to check if a file is a text file? In a script
>> > I could use the `file` command which is not ideal as I have to grep
>> > the result. In Perl I could do  -T file.
>> >
>> > How to do best in Python?  
>> 
>> If you are on Linux and more interested in the result than the
>> programming exercise, I would suggest the following non-Python
>> solution:
>> 
>>find . -type -f -exec sed -i 's/foo/bar/g' {} \;
>> 
>
> My existing script in Perl which I wanted to migrate to Python I used 
>  `-T $file` and called sed
>
> I like the -T which I assume does some heuristics to tell me if a file
> is a text file. 

Sorry, I missed the bit about text files.  By '-T' I assume you mean
Perl's taint mode option.  I am no security expert, but as I understand
it, taint mode does more than just check whether something is a text
file, although the "more" probably applies mainly to files which contain
Perl code.

Sorry also to bang on about non-Python solutions but you could do

  find . -type f -exec grep -Iq . {} \; -and -exec sed -i 's/foo/bar/g' {} \;

i.e. let grep ignore binary files and quietly match all non-binary files.

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Re: Changing strings in files

[Manfred Lotz]

On Tue, 10 Nov 2020 18:52:26 +1100
Mike Dewhirst  wrote:

> On 10/11/2020 5:24 pm, Manfred Lotz wrote:
> > I have a situation where in a directory tree I want to change a
> > certain string in all files where that string occurs.
> >
> > My idea was to do
> >
> > - os.scandir and for each file
> > - check if a file is a text file
> > - if it is not a text file skip that file
> > - change the string as often as it occurs in that file
> >
> >
> > What is the best way to check if a file is a text file? In a script
> > I could use the `file` command which is not ideal as I have to grep
> > the result. In Perl I could do  -T file.
> >
> > How to do best in Python?  
> Not necessarily best but I rolled this earlier. Much earlier. But I 
> still use it. I don't need to worry about text files or binary
> because I specify .py files.
> 
>   
> 
> # -*- coding: utf-8 -*-
> """
> Look for string 'find' and replace it with string 'repl' in all files
> in the current directory and all sub-dirs.
> 
> If anything untoward happens, laboriously retrieve each original file
> from each individual backup made by suffixing ~ to the filename.
> 
> If everything went well, make find == repl and run again to remove
> backups.
> 
> """
> import os
> 
> find = """# Copyright (c) 2019 Xyz Pty Ltd"""
> 
> repl = """# Copyright (c) 2020 Xyz Pty Ltd"""
> 
> ii = 0
> kk = 0
> for dirpath, dirnames, filenames in os.walk(".", topdown=True):
>  if "migrations" in dirpath:
>  continue
>  for filename in filenames:
>  if filename.endswith(".py"):  # or filename.endswith(".txt"):
>  fil = os.path.join(dirpath, filename)
>  bak = "{0}~".format(fil)
>  if find == repl:
>  if os.path.isfile(bak):
>  ii += 1
>  os.remove(bak)
>  else:
>  with open(fil, "r") as src:
>  lines = src.readlines()
>  # make a backup file
>  with open(bak, "w", encoding="utf-8") as dst:
>  for line in lines:
>  dst.write(line)
>  with open(bak, "r") as src:
>  lines = src.readlines()
>  # re-write the original src
>  with open(fil, "w", encoding="utf-8") as dst:
>  kk += 1
>  for line in lines:
>  dst.write(line.replace(find, repl))
> print("\nbak deletions = %s, tried = %s\n" % (ii, kk))
> 
> 

Thanks, will take a look.

-- 
Manfred

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Re: Changing strings in files

[Manfred Lotz]

On Tue, 10 Nov 2020 18:37:54 +1100
Cameron Simpson  wrote:

> On 10Nov2020 07:24, Manfred Lotz  wrote:
> >I have a situation where in a directory tree I want to change a
> >certain string in all files where that string occurs.
> >
> >My idea was to do
> >
> >- os.scandir and for each file  
> 
> Use os.walk for trees. scandir does a single directory.
> 

Perhaps better. I like to use os.scandir this way

def scantree(path: str) -> Iterator[os.DirEntry[str]]:
"""Recursively yield DirEntry objects (no directories)
  for a given directory.
""" 
for entry in os.scandir(path):
if entry.is_dir(follow_symlinks=False):
yield from scantree(entry.path)

yield entry

Worked fine so far. I think I coded it this way because I wanted the
full path of the file the easy way.



> >   - check if a file is a text file  
> 
> This requires reading the entire file. You want to check that it 
> consists entirely of lines of text. In your expected text encoding - 
> these days UTF-8 is the common default, but getting this correct is 
> essential if you want to recognise text. So as a first cut, totally 
> untested:
> 
> ...

The reason I want to check if a file is a text file is that I don't
want to try replacing patterns in binary files (executable binaries,
archives, audio files aso).

Of course, to make this nicely work some heuristic check would be the
right thing (this is what file command does). I am aware that an
heuristic check is not 100% but I think it is good enough.


-- 
Manfred

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Tkinter List of Canvases

[ChalaoAdda]

Hello,

I have a list of canvas of images. I would like to display all the images. But 
it displays the last image. Here is my code.

from tkinter import *
from PIL import Image, ImageTk

root = Tk()

canvas_width = 265
canvas_height = 130
canvases = []

r, c = 0, 0

for tile in tiles:
img = tile.image
photo = ImageTk.PhotoImage(image=img)
can = Canvas(root, width=canvas_width, height=canvas_height)
can.create_image(0, 0, image=photo, anchor=NW)
canvases.append(can)
can.grid(row=r, column=c)

   c += 1
if c % 5 == 0:
r += 1
c = 0


root.mainloop()

Please help.
Thanks.
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Re: Changing strings in files

[Chris Angelico]

On Tue, Nov 10, 2020 at 9:06 PM Manfred Lotz  wrote:
> The reason I want to check if a file is a text file is that I don't
> want to try replacing patterns in binary files (executable binaries,
> archives, audio files aso).
>

I'd recommend two checks, then:

1) Can the file be decoded as UTF-8?
2) Does it contain any NULs?

The checks can be done in either order; you can check if the file
contains any b"\0" or you can check if the decoded text contains any
u"\0", since UTF-8 guarantees that those are the same.

If both those checks pass, it's still possible that the file isn't one
you want to edit, but it is highly likely to be text.

ChrisA
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Re: Changing strings in files

[Cameron Simpson]

On 10Nov2020 10:07, Manfred Lotz  wrote:
>On Tue, 10 Nov 2020 18:37:54 +1100
>Cameron Simpson  wrote:
>> Use os.walk for trees. scandir does a single directory.
>
>Perhaps better. I like to use os.scandir this way
>
>def scantree(path: str) -> Iterator[os.DirEntry[str]]:
>"""Recursively yield DirEntry objects (no directories)
>  for a given directory.
>"""
>for entry in os.scandir(path):
>if entry.is_dir(follow_symlinks=False):
>yield from scantree(entry.path)
>
>yield entry
>
>Worked fine so far. I think I coded it this way because I wanted the
>full path of the file the easy way.

Yes, that's fine and easy to read. Note that this is effectively a 
recursive call though, with the associated costs:

- a scandir (or listdir, whatever) has the directory open, and holds it 
  open while you scan the subdirectories; by contrast os.walk only opens 
  one directory at a time

- likewise, if you're maintaining data during a scan, that is held while 
  you process the subdirectories; with an os.walk you tend to do that 
  and release the memory before the next iteration of the main loop 
  (obviously, depending exactly what you're doing)

However, directory trees tend not to be particularly deep, and the depth 
governs the excess state you're keeping around.

>> >   - check if a file is a text file
>>
>> This requires reading the entire file. You want to check that it
>> consists entirely of lines of text. In your expected text encoding -
>> these days UTF-8 is the common default, but getting this correct is
>> essential if you want to recognise text. So as a first cut, totally
>> untested:
>>
>> ...
>
>The reason I want to check if a file is a text file is that I don't
>want to try replacing patterns in binary files (executable binaries,
>archives, audio files aso).

Exactly, which is why you should not trust, say, the "file" utility. It 
scans only the opening part of the file. Great for rejecting files, but 
not reliable for being _sure_ about the whole file being text when it 
doesn't reject.

>Of course, to make this nicely work some heuristic check would be the
>right thing (this is what file command does). I am aware that an
>heuristic check is not 100% but I think it is good enough.

Shrug. That is a risk you must evaluate yourself. I'm quite paranoid 
about data loss, myself. If you've got backups or are working on copies 
the risks are mitigated.

You could perhaps take a more targeted approach: do your target files 
have distinctive file extensions (for example, all the .py files in a 
source tree).

Cheers,
Cameron Simpson 
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Re: Changing strings in files

[Grant Edwards]

On 2020-11-10, Manfred Lotz  wrote:

> What is the best way to check if a file is a text file?

Step 1: define "text file"

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ANN: DIPY 1.3.0

[Eleftherios Garyfallidis]

Hello all,

We are excited to announce a new release of DIPY: DIPY 1.3 is out!

Please support us by citing DIPY in your papers using the following DOI:
10.3389/fninf.2014.8  

DIPY 1.3.0 (Wednesday, 3 November 2020)

This release received contributions from 27 developers (the full release
notes are at:
https://dipy.org/documentation/1.3.0./release_notes/release1.3/). Thank you
all for your contributions and feedback!

Please click here  to
check API changes.

Highlights of this release include:

- Gibbs ringing correction 10X faster.

- Spherical harmonics basis definitions updated.

- Added SMT2 metrics from mean signal diffusion kurtosis.

- New interface functions added to the registration module.

- New linear transform added to the registration module.

- New tutorials for DIPY command line interfaces.

- Fixed compatibility issues with different dependencies.

- Tqdm (multiplatform progress bar) dependency added.

- Large documentation update.

- Bundle section highlight from BUAN added in Horizon.

- Closed 134 issues and merged 49 pull requests.

Note:

Have in mind that DIPY does not support Python 2 after version 0.16.0. All
major Python projects have switched to Python 3. It is time that you switch
too.


To upgrade or install  DIPY

Run the following command in your terminal:


pip install --upgrade dipy

or

conda install -c conda-forge dipy

This version of DIPY depends on nibabel (3.0.0+).

For visualization you need FURY (0.6.1+).

Questions or suggestions?



For any questions go to https://dipy.org, or send an e-mail to
d...@python.org 

We also have an instant messaging service and chat room available at
https://gitter.im/dipy/dipy

On behalf of the DIPY developers,

Eleftherios Garyfallidis, Ariel Rokem, Serge Koudoro

https://dipy.org/contributors
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constant folding - why not more

[David Kolovratník]

Dear all,

I would like to learn about constant folding optimisation in Python. It seems
to be implemented in Python/ast_opt.c. In order to get impression I used
python3 and dis module:

$ python3 -V
Python 3.7.3

Arithmetics expression is folded as expected:

>>> dis.dis(compile('1 * 2', filename='', mode='eval',
>>> optimize=2))
  1   0 LOAD_CONST   0 (2)
  2 RETURN_VALUE

On the contrary, comparison remains for runtime:
>>> dis.dis(compile('1 < 2', filename='', mode='eval',
>>> optimize=2))
  1   0 LOAD_CONST   0 (1)
  2 LOAD_CONST   1 (2)
  4 COMPARE_OP   0 (<)
  6 RETURN_VALUE
In function fold_unaryop (though comparison is a binary operation) in
Python/ast_opt.c is remark: /* Fold not into comparison */

Is there a reason why comparison (== != < > <= >=) is not folded? I would
expect it handled in fold_binop.

Besides comparison there are other expressions that might be optimized out 
due to constant expression. Ternary operator with constant condition True
has IF optimized out (just some dead code remains):
>>> dis.dis(compile('"a" if True else "b"', filename='',
>>> mode='eval', optimize=2))
  1   0 LOAD_CONST   1 ('a')
  2 RETURN_VALUE
  4 LOAD_CONST   2 ('b')
  6 RETURN_VALUE

On the contrary, the same ternary operator with constant condition False
still loads the constat and contains POP_JUMP_IF_FALSE:
>>> dis.dis(compile('"a" if False else "b"', filename='',
>>> mode='eval', optimize=2))
  1   0 LOAD_CONST   0 (False)
  2 POP_JUMP_IF_FALSE8
  4 LOAD_CONST   1 ('a')
  6 RETURN_VALUE
>>8 LOAD_CONST   2 ('b')
 10 RETURN_VALUE

Any ideas or links, please?

Best regards,
Davis
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Re: Tkinter List of Canvases

[MRAB]

On 2020-11-10 10:01, ChalaoAdda wrote:

Hello,

I have a list of canvas of images. I would like to display all the images. But 
it displays the last image. Here is my code.

from tkinter import *
from PIL import Image, ImageTk

root = Tk()

canvas_width = 265
canvas_height = 130
canvases = []

r, c = 0, 0

for tile in tiles:
 img = tile.image
 photo = ImageTk.PhotoImage(image=img)
 can = Canvas(root, width=canvas_width, height=canvas_height)
 can.create_image(0, 0, image=photo, anchor=NW)
 canvases.append(can)
 can.grid(row=r, column=c)

c += 1
 if c % 5 == 0:
 r += 1
 c = 0


root.mainloop()

You need to keep a reference to the images. In your code, 'photo' still 
refers to the last photoimage, so that's why it's displayed; there are 
no references to the others, so they're garbage-collected. (You probably 
expected that 'create_image' would keep a reference to the image, but it 
doesn't. tkinter has its idiosyncrasies!)


Try adding a list for the photoimages:

...
photos = []

for tile in tiles:
img = tile.image
photo = ImageTk.PhotoImage(image=img)
photos.append(photo)
can = Canvas(root, width=canvas_width, height=canvas_height)
...
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Re: constant folding - why not more

[Barry Scott]

> On 10 Nov 2020, at 14:45, David Kolovratník  wrote:
> 
> Dear all,
> 
> I would like to learn about constant folding optimisation in Python. It seems
> to be implemented in Python/ast_opt.c. In order to get impression I used
> python3 and dis module:
> 
> $ python3 -V
> Python 3.7.3

I do not have answers to your questions, but I would suggest that you look at 
3.9
or even 3.10a2 to see if this is still the case.

Barry

> 
> Arithmetics expression is folded as expected:
> 
 dis.dis(compile('1 * 2', filename='', mode='eval',
 optimize=2))
>  1   0 LOAD_CONST   0 (2)
>  2 RETURN_VALUE
> 
> On the contrary, comparison remains for runtime:
 dis.dis(compile('1 < 2', filename='', mode='eval',
 optimize=2))
>  1   0 LOAD_CONST   0 (1)
>  2 LOAD_CONST   1 (2)
>  4 COMPARE_OP   0 (<)
>  6 RETURN_VALUE
> In function fold_unaryop (though comparison is a binary operation) in
> Python/ast_opt.c is remark: /* Fold not into comparison */
> 
> Is there a reason why comparison (== != < > <= >=) is not folded? I would
> expect it handled in fold_binop.
> 
> Besides comparison there are other expressions that might be optimized out 
> due to constant expression. Ternary operator with constant condition True
> has IF optimized out (just some dead code remains):
 dis.dis(compile('"a" if True else "b"', filename='',
 mode='eval', optimize=2))
>  1   0 LOAD_CONST   1 ('a')
>  2 RETURN_VALUE
>  4 LOAD_CONST   2 ('b')
>  6 RETURN_VALUE
> 
> On the contrary, the same ternary operator with constant condition False
> still loads the constat and contains POP_JUMP_IF_FALSE:
 dis.dis(compile('"a" if False else "b"', filename='',
 mode='eval', optimize=2))
>  1   0 LOAD_CONST   0 (False)
>  2 POP_JUMP_IF_FALSE8
>  4 LOAD_CONST   1 ('a')
>  6 RETURN_VALUE
>>>   8 LOAD_CONST   2 ('b')
> 10 RETURN_VALUE
> 
> Any ideas or links, please?
> 
> Best regards,
> Davis
> -- 
> https://mail.python.org/mailman/listinfo/python-list
> 

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Re: Changing strings in files

[Eli the Bearded]

In comp.lang.python, Loris Bennett  wrote:
> Manfred Lotz  writes:
> > My idea was to do
> >
> > - os.scandir and for each file
> >- check if a file is a text file
 ^^
> >- if it is not a text file skip that file
> >- change the string as often as it occurs in that file
> >
> > What is the best way to check if a file is a text file? In a script I
^^^
> > could use the `file` command which is not ideal as I have to grep the
> > result. In Perl I could do  -T file.
> If you are on Linux and more interested in the result than the
> programming exercise, I would suggest the following non-Python solution:
> 
>find . -type -f -exec sed -i 's/foo/bar/g' {} \;

That 100% fails the "check if a text file" part.

> Having said that, I would be interested to know what the most compact
> way of doing the same thing in Python might be.

Read first N lines of a file. If all parse as valid UTF-8, consider it text.
That's probably the rough method file(1) and Perl's -T use. (In
particular allow no nulls. Maybe allow ISO-8859-1.)

Elijah
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Re: Changing strings in files

[Chris Angelico]

On Wed, Nov 11, 2020 at 5:36 AM Eli the Bearded <*@eli.users.panix.com> wrote:
> Read first N lines of a file. If all parse as valid UTF-8, consider it text.
> That's probably the rough method file(1) and Perl's -T use. (In
> particular allow no nulls. Maybe allow ISO-8859-1.)
>

ISO-8859-1 is basically "allow any byte values", so all you'd be doing
is checking for a lack of NUL bytes. I'd definitely recommend
mandating UTF-8, as that's a very good way of recognizing valid text,
but if you can't do that then the simple NUL check is all you really
need.

And let's be honest here, there aren't THAT many binary files that
manage to contain a total of zero NULs, so you won't get many false
hits :)

ChrisA
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Re: Changing strings in files

[Manfred Lotz]

On Tue, 10 Nov 2020 22:08:54 +1100
Cameron Simpson  wrote:

> On 10Nov2020 10:07, Manfred Lotz  wrote:
> >On Tue, 10 Nov 2020 18:37:54 +1100
> >Cameron Simpson  wrote:  
> >> Use os.walk for trees. scandir does a single directory.  
> >
> >Perhaps better. I like to use os.scandir this way
> >
> >def scantree(path: str) -> Iterator[os.DirEntry[str]]:
> >"""Recursively yield DirEntry objects (no directories)
> >  for a given directory.
> >"""
> >for entry in os.scandir(path):
> >if entry.is_dir(follow_symlinks=False):
> >yield from scantree(entry.path)
> >
> >yield entry
> >
> >Worked fine so far. I think I coded it this way because I wanted the
> >full path of the file the easy way.  
> 
> Yes, that's fine and easy to read. Note that this is effectively a 
> recursive call though, with the associated costs:
> 
> - a scandir (or listdir, whatever) has the directory open, and holds
> it open while you scan the subdirectories; by contrast os.walk only
> opens one directory at a time
> 
> - likewise, if you're maintaining data during a scan, that is held
> while you process the subdirectories; with an os.walk you tend to do
> that and release the memory before the next iteration of the main
> loop (obviously, depending exactly what you're doing)
> 
> However, directory trees tend not to be particularly deep, and the
> depth governs the excess state you're keeping around.
> 

Very interesting information. Thanks a lot for this. I will take a
closer look at os.walk.

> >> >   - check if a file is a text file  
> >>
> >> This requires reading the entire file. You want to check that it
> >> consists entirely of lines of text. In your expected text encoding
> >> - these days UTF-8 is the common default, but getting this correct
> >> is essential if you want to recognise text. So as a first cut,
> >> totally untested:
> >>
> >> ...  
> >
> >The reason I want to check if a file is a text file is that I don't
> >want to try replacing patterns in binary files (executable binaries,
> >archives, audio files aso).  
> 
> Exactly, which is why you should not trust, say, the "file" utility.
> It scans only the opening part of the file. Great for rejecting
> files, but not reliable for being _sure_ about the whole file being
> text when it doesn't reject.
> 
> >Of course, to make this nicely work some heuristic check would be the
> >right thing (this is what file command does). I am aware that an
> >heuristic check is not 100% but I think it is good enough.  
> 
> Shrug. That is a risk you must evaluate yourself. I'm quite paranoid 
> about data loss, myself. If you've got backups or are working on
> copies the risks are mitigated.
> 
> You could perhaps take a more targeted approach: do your target files 
> have distinctive file extensions (for example, all the .py files in a 
> source tree).
> 

There are some distinctive file extensions. The reason I am satisfieg
with heuristics is that the string to change is pretty long so that
there is no real danger if I try to change in a binary file because
that string it not to be found in binary files. 

The idea to skip binary files was simply to save time. 

-- 
Manfred








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Re: Changing strings in files

[Manfred Lotz]

On Tue, 10 Nov 2020 10:57:05 +0100
"Loris Bennett"  wrote:

> Manfred Lotz  writes:
> 
> > On Tue, 10 Nov 2020 08:19:55 +0100
> > "Loris Bennett"  wrote:
> >  
> >> Manfred Lotz  writes:
> >>   
> >> > I have a situation where in a directory tree I want to change a
> >> > certain string in all files where that string occurs.
> >> >
> >> > My idea was to do
> >> >
> >> > - os.scandir and for each file
> >> >- check if a file is a text file
> >> >- if it is not a text file skip that file
> >> >- change the string as often as it occurs in that file
> >> >
> >> >
> >> > What is the best way to check if a file is a text file? In a
> >> > script I could use the `file` command which is not ideal as I
> >> > have to grep the result. In Perl I could do  -T file.
> >> >
> >> > How to do best in Python?
> >> 
> >> If you are on Linux and more interested in the result than the
> >> programming exercise, I would suggest the following non-Python
> >> solution:
> >> 
> >>find . -type -f -exec sed -i 's/foo/bar/g' {} \;
> >>   
> >
> > My existing script in Perl which I wanted to migrate to Python I
> > used `-T $file` and called sed
> >
> > I like the -T which I assume does some heuristics to tell me if a
> > file is a text file.   
> 
> Sorry, I missed the bit about text files.  By '-T' I assume you mean
> Perl's taint mode option.  I am no security expert, but as I
> understand it, taint mode does more than just check whether something
> is a text file, although the "more" probably applies mainly to files
> which contain Perl code.
> 
> Sorry also to bang on about non-Python solutions but you could do
> 
>   find . -type f -exec grep -Iq . {} \; -and -exec sed -i
> 's/foo/bar/g' {} \;
> 
> i.e. let grep ignore binary files and quietly match all non-binary
> files.
> 

Very nice. Thanks for this.

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Re: Changing strings in files

[Eli the Bearded]

In comp.lang.python, Chris Angelico  wrote:
> Eli the Bearded <*@eli.users.panix.com> wrote:
>> Read first N lines of a file. If all parse as valid UTF-8, consider it text.
>> That's probably the rough method file(1) and Perl's -T use. (In
>> particular allow no nulls. Maybe allow ISO-8859-1.)
> ISO-8859-1 is basically "allow any byte values", so all you'd be doing
> is checking for a lack of NUL bytes.

ISO-8859-1, unlike similar Windows "charset"s, does not use octets
128-190. Charsets like Windows CP-1252 are nastier, because they do
use that range. Usage of 1-31 will be pretty restricted in either,
probably not more than tab, linefeed, and carriage return.

> I'd definitely recommend
> mandating UTF-8, as that's a very good way of recognizing valid text,
> but if you can't do that then the simple NUL check is all you really
> need.

Dealing with all UTF-8 is my preference, too.

> And let's be honest here, there aren't THAT many binary files that
> manage to contain a total of zero NULs, so you won't get many false
> hits :)

There's always the issue of how much to read before deciding.

Elijah
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Re: Changing strings in files

[Barry Scott]

> On 10 Nov 2020, at 19:30, Eli the Bearded <*@eli.users.panix.com> wrote:
> 
> In comp.lang.python, Chris Angelico  wrote:
>> Eli the Bearded <*@eli.users.panix.com> wrote:
>>> Read first N lines of a file. If all parse as valid UTF-8, consider it text.
>>> That's probably the rough method file(1) and Perl's -T use. (In
>>> particular allow no nulls. Maybe allow ISO-8859-1.)
>> ISO-8859-1 is basically "allow any byte values", so all you'd be doing
>> is checking for a lack of NUL bytes.

NUL check does not work for windows UTF-16 files.

> 
> ISO-8859-1, unlike similar Windows "charset"s, does not use octets
> 128-190. Charsets like Windows CP-1252 are nastier, because they do
> use that range. Usage of 1-31 will be pretty restricted in either,
> probably not more than tab, linefeed, and carriage return.

Who told you that?

The C1 control plane is used in ISO 8 bit char sets.

One optimisation for the Vt100 family of terminals is to send CSI as 0x8b
and not as 0x1b '['. Back in the days of 9600 bps or 1200 bps connections
that was worth the effort.

> 
>> I'd definitely recommend
>> mandating UTF-8, as that's a very good way of recognizing valid text,
>> but if you can't do that then the simple NUL check is all you really
>> need.
> 
> Dealing with all UTF-8 is my preference, too.
> 
>> And let's be honest here, there aren't THAT many binary files that
>> manage to contain a total of zero NULs, so you won't get many false
>> hits :)

There is the famous EICAR virus test file that is a valid 8086 program for
DOS that is printing ASCII.

> 
> There's always the issue of how much to read before deciding.

Simple read it all, after all you have to scan all the file to do the 
replacement.

> 
> Elijah
> --
> ASCII with embedded escapes? could be a VT100 animation

The output of software that colours its logs maybe?

Barry

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> 

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Re: constant folding - why not more

[Terry Reedy]

On 11/10/2020 1:03 PM, Barry Scott wrote:




On 10 Nov 2020, at 14:45, David Kolovratník  wrote:

Dear all,

I would like to learn about constant folding optimisation in Python. It seems
to be implemented in Python/ast_opt.c. In order to get impression I used
python3 and dis module:

$ python3 -V
Python 3.7.3


I do not have answers to your questions, but I would suggest that you look at 
3.9
or even 3.10a2 to see if this is still the case.


Checking with 3.10...


Arithmetics expression is folded as expected:


dis.dis(compile('1 * 2', filename='', mode='eval',
optimize=2))

  1   0 LOAD_CONST   0 (2)
  2 RETURN_VALUE

On the contrary, comparison remains for runtime:

dis.dis(compile('1 < 2', filename='', mode='eval',
optimize=2))

  1   0 LOAD_CONST   0 (1)
  2 LOAD_CONST   1 (2)
  4 COMPARE_OP   0 (<)
  6 RETURN_VALUE


Same.


In function fold_unaryop (though comparison is a binary operation) in
Python/ast_opt.c is remark: /* Fold not into comparison */


Use git blame to find out who and when made that remark.


Is there a reason why comparison (== != < > <= >=) is not folded? I would
expect it handled in fold_binop.

Besides comparison there are other expressions that might be optimized out
due to constant expression. Ternary operator with constant condition True
has IF optimized out (just some dead code remains):

dis.dis(compile('"a" if True else "b"', filename='',
mode='eval', optimize=2))

  1   0 LOAD_CONST   1 ('a')
  2 RETURN_VALUE


Remains.


  4 LOAD_CONST   2 ('b')
  6 RETURN_VALUE


Gone.


On the contrary, the same ternary operator with constant condition False
still loads the constat and contains POP_JUMP_IF_FALSE:

dis.dis(compile('"a" if False else "b"', filename='',
mode='eval', optimize=2))

  1   0 LOAD_CONST   0 (False)
  2 POP_JUMP_IF_FALSE8
  4 LOAD_CONST   1 ('a')
  6 RETURN_VALUE
>>8 LOAD_CONST   2 ('b')
 10 RETURN_VALUE


Same.  You could file issue for this, but one guess is that else clause 
might spill over to another line, and current decision is that for 
tracing, every line of code that naively should be executed is executed 
rather than optimized away.  But I would first try to find the file that 
produces bytecode and then use git blame to find issue where the True 
else part was removed.


--
Terry Jan Reedy


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Re: Changing strings in files

[Chris Angelico]

On Wed, Nov 11, 2020 at 6:36 AM Eli the Bearded <*@eli.users.panix.com> wrote:
>
> In comp.lang.python, Chris Angelico  wrote:
> > Eli the Bearded <*@eli.users.panix.com> wrote:
> >> Read first N lines of a file. If all parse as valid UTF-8, consider it 
> >> text.
> >> That's probably the rough method file(1) and Perl's -T use. (In
> >> particular allow no nulls. Maybe allow ISO-8859-1.)
> > ISO-8859-1 is basically "allow any byte values", so all you'd be doing
> > is checking for a lack of NUL bytes.
>
> ISO-8859-1, unlike similar Windows "charset"s, does not use octets
> 128-190. Charsets like Windows CP-1252 are nastier, because they do
> use that range. Usage of 1-31 will be pretty restricted in either,
> probably not more than tab, linefeed, and carriage return.

Define "does not use", though. You can decode those bytes just fine:

>>> bytes(range(256)).decode("ISO-8859-1")
'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f
!"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0¡¢£¤¥¦§¨©ª«¬\xad®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ'

This is especially true of \x01 to \x1F, since they are most
definitely defined, even though they aren't commonly used.

> > I'd definitely recommend
> > mandating UTF-8, as that's a very good way of recognizing valid text,
> > but if you can't do that then the simple NUL check is all you really
> > need.
>
> Dealing with all UTF-8 is my preference, too.
>
> > And let's be honest here, there aren't THAT many binary files that
> > manage to contain a total of zero NULs, so you won't get many false
> > hits :)
>
> There's always the issue of how much to read before deciding.
>

Right; but a lot of binary file formats are going to include
structured data that will frequently include a NUL byte. For instance,
a PNG file (after the header) consists of chunks, where each chunk is
identified by a four-byte size; and the first chunk (IHDR) is
generally going to be a very short one, meaning that its size will
generally have three NULs. So a typical PNG file will have a NUL
probably as the ninth byte of the file. Other file formats will be
similar, or even better; an ELF binary actually has a sixteen byte
header of which the last few bytes are reserved for future expansion
and must be zeroes, so that's an even stronger guarantee.

If the main job of the program, as in this situation, is to read the
entire file, I would probably have it read in the first 1KB or 16KB or
thereabouts, see if that has any NUL bytes, and if not, proceed to
read in the rest of the file. But depending on the situation, I might
actually have a hard limit on the file size (say, "any file over 1GB
isn't what I'm looking for"), so that would reduce the risks too.

ChrisA
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Re: Changing strings in files

[Chris Angelico]

On Wed, Nov 11, 2020 at 6:52 AM Barry Scott  wrote:
>
>
>
> > On 10 Nov 2020, at 19:30, Eli the Bearded <*@eli.users.panix.com> wrote:
> >
> > In comp.lang.python, Chris Angelico  wrote:
> >> Eli the Bearded <*@eli.users.panix.com> wrote:
> >>> Read first N lines of a file. If all parse as valid UTF-8, consider it 
> >>> text.
> >>> That's probably the rough method file(1) and Perl's -T use. (In
> >>> particular allow no nulls. Maybe allow ISO-8859-1.)
> >> ISO-8859-1 is basically "allow any byte values", so all you'd be doing
> >> is checking for a lack of NUL bytes.
>
> NUL check does not work for windows UTF-16 files.

Yeah, so if you're expecting UTF-16, you would have to do the decode
to text first, and the check for NULs second. One of the big
advantages of UTF-8 is that you can do the checks in either order.

> >> And let's be honest here, there aren't THAT many binary files that
> >> manage to contain a total of zero NULs, so you won't get many false
> >> hits :)
>
> There is the famous EICAR virus test file that is a valid 8086 program for
> DOS that is printing ASCII.

Yes. I didn't say "none", I said "aren't many" :) There's
fundamentally no way to know whether something is or isn't text based
on its contents alone; raw audio data might just happen to look like
an RFC822 email, it's just really really unlikely.

> > There's always the issue of how much to read before deciding.
>
> Simple read it all, after all you have to scan all the file to do the 
> replacement.

If the script's assuming it'll mostly work on small text files, it
might be very annoying to suddenly read in a 4GB blob of video file
just to find out that it's not text. But since we're talking
heuristics here, reading in a small chunk of the file is going to give
an extremely high chance of recognizing a binary file, with a
relatively small cost.

ChrisA
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Re: constant folding - why not more

[Chris Angelico]

On Wed, Nov 11, 2020 at 4:01 AM David Kolovratník  wrote:
> On the contrary, comparison remains for runtime:
> >>> dis.dis(compile('1 < 2', filename='', mode='eval',
> >>> optimize=2))
>   1   0 LOAD_CONST   0 (1)
>   2 LOAD_CONST   1 (2)
>   4 COMPARE_OP   0 (<)
>   6 RETURN_VALUE
> In function fold_unaryop (though comparison is a binary operation) in
> Python/ast_opt.c is remark: /* Fold not into comparison */
>
> Is there a reason why comparison (== != < > <= >=) is not folded? I would
> expect it handled in fold_binop.

I think that comment is unrelated. It's more about this:

>>> dis.dis(lambda x, y: x is y)
  1   0 LOAD_FAST0 (x)
  2 LOAD_FAST1 (y)
  4 IS_OP0
  6 RETURN_VALUE
>>> dis.dis(lambda x, y: not (x is y))
  1   0 LOAD_FAST0 (x)
  2 LOAD_FAST1 (y)
  4 IS_OP1
  6 RETURN_VALUE
>>> dis.dis(lambda x, y: x is not y)
  1   0 LOAD_FAST0 (x)
  2 LOAD_FAST1 (y)
  4 IS_OP1
  6 RETURN_VALUE

The leading "not" gets folded into the operator, since there's
absolutely no way for "x is not y" and "not (x is y)" to return
different results. Same is true for "not (x in y)".

ChrisA
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Re: Changing strings in files

[Cameron Simpson]

On 11Nov2020 07:25, Chris Angelico  wrote:
>If the main job of the program, as in this situation, is to read the
>entire file, I would probably have it read in the first 1KB or 16KB or
>thereabouts, see if that has any NUL bytes, and if not, proceed to
>read in the rest of the file. But depending on the situation, I might
>actually have a hard limit on the file size (say, "any file over 1GB
>isn't what I'm looking for"), so that would reduce the risks too.

You could shoehorn my suggested code for this efficiently.

It had a loop body like this:

 is_text = False
 try:
 # expect utf-8, fail if non-utf-8 bytes encountered
 with open(filename, encoding='utf-8', errors='strict') as f:
 for lineno, line in enumerate(f, 1):
 ... other checks on each line of the file ...
 if not line.endswith('\n'):
 raise ValueError("line %d: no trailing newline" lineno)
 if str.isprintable(line[:-1]):
 raise ValueError("line %d: not all printable" % lineno)
 # if we get here all checks passed, consider the file 
 # to
 # be text
 is_text = True
 except Exception as e:
 print(filename, "not text", e)
 if not is_text:
 print("skip", filename)
 continue

which scans the entire file to see if it is all text (criteria to be 
changed to suit the user, but I was going for clean strict utf-8 decode, 
all chars "printable").  Since we're doing that, we could accumulate the 
lines as we went and make the replacement in memory. If we get all the 
way out the bottom, rewrite the file.

If memory is a concern, we could copy modified lines to a temporary 
file, and copy back if everything was good (or not if we make no 
replacements).

Cheers,
Cameron Simpson 
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Re: Changing strings in files

[Cameron Simpson]

On 11Nov2020 07:30, Chris Angelico  wrote:
>If the script's assuming it'll mostly work on small text files, it
>might be very annoying to suddenly read in a 4GB blob of video file
>just to find out that it's not text.

You can abort as soon as the decode fails. Which will usually be pretty 
early for video.

Cheers,
Cameron Simpson 
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Re: Changing strings in files

[Chris Angelico]

On Wed, Nov 11, 2020 at 10:00 AM Cameron Simpson  wrote:
>
> On 11Nov2020 07:30, Chris Angelico  wrote:
> >If the script's assuming it'll mostly work on small text files, it
> >might be very annoying to suddenly read in a 4GB blob of video file
> >just to find out that it's not text.
>
> You can abort as soon as the decode fails. Which will usually be pretty
> early for video.
>
Only if you haven't already read it from the file system, which is the
point of the early abort :)

ChrisA
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ctypes struct alignment specification

[Chris]

I am working on a CUDA python API using ctypes. Within CUDA there are vector 
type structs defined (float2, float3, float4, int2, int3, int4, ...), all of 
which have an alignment specification (example of how this is specified 
https://stackoverflow.com/questions/12778949/cuda-memory-alignment/12779757) . 
I want to include these structs in the Python api but as far as I can tell, 
ctypes does not have a way to specify a structure's alignment in the same 
fashion (the #pragma pack(n) alignment feature that ctypes does support does 
not do the same thing). If the alignment specification is omitted on the Python 
side, the structure's alignment can be mismatched between the host (CPU) and 
device (GPU) causing segfaults/etc. . Is this something that could be added to 
ctypes or is it not feasible/possible?
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Re: constant folding - why not more

[Skip Montanaro]

>
> On the contrary, comparison remains for runtime:
> >>> dis.dis(compile('1 < 2', filename='', mode='eval',
> >>> optimize=2))
>   1   0 LOAD_CONST   0 (1)
>   2 LOAD_CONST   1 (2)
>   4 COMPARE_OP   0 (<)
>   6 RETURN_VALUE
> In function fold_unaryop (though comparison is a binary operation) in
> Python/ast_opt.c is remark: /* Fold not into comparison */
>
> Is there a reason why comparison (== != < > <= >=) is not folded?
>

I can think of two reasons. One, this kind of comparison will almost never
appear in production code (maybe in unit tests?). Unlike the C family of
languages, Python doesn't have a macro processor which would give symbolic
names to numeric constants or string literals. Code generators might
conceivably generate constant comparisons, but they might be able to easily
do constant folding of comparisons themselves.

Two, given that this sort of construct will almost never be found in the
wild, folding constant comparisons in the compiler would increase the
maintenance burden of the compiler (just slightly, but still...) with no
clear benefit.

Skip

>
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Problem with rearanging list with paired letters next to each others

[Bischoop]

Can anybody help?Here's the code that gives me a hedeache for second day 
https://bpa.st/XLOA 
If I have letter_list = ["a","a",,"b","b","c","c"] it's working
correctly but if I have three or more of any letters for
example:letter_list = ["a","a","a","b","b","c","c"], I'm ending up with
some pairs somewhere.
I took another way approach today: https://bpa.st/E7HQ, was thinking
about iterating and checking if neighbour characters won't make a pair
but I've end up with error:
if x != letter_list[i+1] and letter_list[i-1]:
IndexError: list index out of range
andin addition: got 4 "a" (had 3only) and missing 1 "b" :-/

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Re: Problem with rearanging list with paired letters next to each others

[MRAB]

On 2020-11-11 01:26, Bischoop wrote:


Can anybody help?Here's the code that gives me a hedeache for second day 
https://bpa.st/XLOA
If I have letter_list = ["a","a",,"b","b","c","c"] it's working
correctly but if I have three or more of any letters for
example:letter_list = ["a","a","a","b","b","c","c"], I'm ending up with
some pairs somewhere.
I took another way approach today: https://bpa.st/E7HQ, was thinking
about iterating and checking if neighbour characters won't make a pair
but I've end up with error:
if x != letter_list[i+1] and letter_list[i-1]:
IndexError: list index out of range
andin addition: got 4 "a" (had 3only) and missing 1 "b" :-/


Points to note in your first code:

1. Modifying a list while iterating over it is a bad idea.

2. You're modifying the list that you're passing in and also returning 
it. That's a bad idea. Either modify it in place or modify and return a 
copy.


3. The line:

   m = (letter_list.index(x))

   returns the position of the first occurrence of x.

Points to note in your second code:

1. (See above)

2. (See above)

3. (See above)

4. 'i' goes from 0 to len(letter_list)-1, so i+1 goes from 1 to 
len(letter_list), but the maximum index permitted by letter_list is 
len(letter_list)-1, hence letter_list[i+1] will raise IndexError on the 
last iteration.


5. 'i' goes from 0 to len(letter_list)-1, so i-1 goes from -1 to 
len(letter_list)-2. letter_list[-1] returns the last (final) letter in 
the list, and it's treated as a true.


6. This:

   x != letter_list[i+1] and letter_list[i-1]

   is checking whether:

   x != letter_list[i+1]

   is true and also whether:

   letter_list[i-1]

   is true.
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Re: Tkinter List of Canvases

[ChalaoAdda]

On Tue, 10 Nov 2020 17:21:04 +, MRAB wrote:

> On 2020-11-10 10:01, ChalaoAdda wrote:
>> Hello,
>> 
>> I have a list of canvas of images. I would like to display all the
>> images. But it displays the last image. Here is my code.
>> 
>> from tkinter import *
>> from PIL import Image, ImageTk
>> 
>> root = Tk()
>> 
>> canvas_width = 265 canvas_height = 130 canvases = []
>> 
>> r, c = 0, 0
>> 
>> for tile in tiles:
>>  img = tile.image photo = ImageTk.PhotoImage(image=img)
>>  can = Canvas(root, width=canvas_width, height=canvas_height)
>>  can.create_image(0, 0, image=photo, anchor=NW)
>>  canvases.append(can)
>>  can.grid(row=r, column=c)
>> 
>> c += 1
>>  if c % 5 == 0:
>>  r += 1 c = 0
>> 
>> 
>> root.mainloop()
>> 
> You need to keep a reference to the images. In your code, 'photo' still
> refers to the last photoimage, so that's why it's displayed; there are
> no references to the others, so they're garbage-collected. (You probably
> expected that 'create_image' would keep a reference to the image, but it
> doesn't. tkinter has its idiosyncrasies!)
> 
> Try adding a list for the photoimages:
> 
> ...
> photos = []
> 
> for tile in tiles:
>  img = tile.image photo = ImageTk.PhotoImage(image=img)
>  photos.append(photo)
>  can = Canvas(root, width=canvas_width, height=canvas_height)
> ...

Thanks a lot.

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