Re: [Tutor] When you think to setup the __class__ of a module object to a subclass of ModuleType
On 25/04/19 3:52 AM, Alan Gauld via Tutor wrote:
On 24/04/2019 12:22, Arup Rakshit wrote:
In the simple code like what are the advantages we get from?
I'm not really sure what you are asking about?
Ok. My question is that when people add such a class to the module? What
is the goal/intention they met by setting such __class__ attribute of a
module. The documentation I am reading just shown this technique but
didn't dig into this. They didn't explain why/when should we use this
technique, but the how.
Is this so that we can implement more special methods
than just __getattr__ and __dir__ in the module level?
Is it just the inheritance from ModuleType?
Or is it the assignment of the __class__ attribute?
Yes the reason of this assignment.
Or something else?
import sys
from types import ModuleType
class VerboseModule(ModuleType):
def __repr__(self):
return f'Verbose {self.__name__}'
def __setattr__(self, attr, value):
print(f'Setting {attr}...')
super().__setattr__(attr, value)
sys.modules[__name__].__class__ = VerboseModule
There are many things in Python that are not generally used
by ordinary Python programmers. In many cases these are things
used by the core developers or are intended for advanced meta
programming type tasks. As a general rule of thumb any time
you see code that accesses dunder attributes (ie those with
leading and trailing __ markers) directly it's probably an
advanced technique you are unlikely to ever need...
That's a good catch. I am currently reading
https://docs.python.org/3/reference/index.html source, and it seems like
they touched everything possible in Python, without saying which is
advance and which is basic part. Very often I get stuck, and coming here
to ask and understand it. As the author didn't give the hints anything
about what is advanced part, I am assuming these all a Python developer
should know irrespective of their years of Python experience and keep
readiing. But it feels like a lot in one go.
But if you want to increase your understanding carry on
asking but please be as specific as possible about what
it is you want the answer to.
--
Thanks,
Arup Rakshit
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Re: [Tutor] When you think to setup the __class__ of a module object to a subclass of ModuleType
On Thu, Apr 25, 2019 at 11:30:28AM +0530, Arup Rakshit wrote: > On 25/04/19 3:52 AM, Alan Gauld via Tutor wrote: > >On 24/04/2019 12:22, Arup Rakshit wrote: > >>In the simple code like what are the advantages we get from? > >I'm not really sure what you are asking about? > > Ok. My question is that when people add such a class to the module? What > is the goal/intention they met by setting such __class__ attribute of a > module. The documentation I am reading just shown this technique but > didn't dig into this. They didn't explain why/when should we use this > technique, but the how. Can to share which documentation you are reading? I've been using Python since version 1.5, and I've never heard of this technique. Thanks. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] When you think to setup the __class__ of a module object to a subclass of ModuleType
On 25/04/19 1:21 PM, Steven D'Aprano wrote: On Thu, Apr 25, 2019 at 11:30:28AM +0530, Arup Rakshit wrote: On 25/04/19 3:52 AM, Alan Gauld via Tutor wrote: On 24/04/2019 12:22, Arup Rakshit wrote: In the simple code like what are the advantages we get from? I'm not really sure what you are asking about? Ok. My question is that when people add such a class to the module? What is the goal/intention they met by setting such __class__ attribute of a module. The documentation I am reading just shown this technique but didn't dig into this. They didn't explain why/when should we use this technique, but the how. Can to share which documentation you are reading? I've been using Python since version 1.5, and I've never heard of this technique. Thanks. Hello Steven, Here it is: *3.3.2.1. Customizing module attribute access* (https://docs.python.org/3/reference/datamodel.html#customizing-module-attribute-access) -- Thanks, Arup Rakshit ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] module import from a packager works inconsistent between REPL and command line
I have a small app like this:
pizza-shop$ tree .
.
└── pizzapy
├── __init__.py
├── menu.py
└── pizza.py
1 directory, 3 files
# menu.py
from typing import List
from pizza import Pizza
MENU: List[Pizza] = [
Pizza('Margherita', 30, 10.0),
Pizza('Carbonara', 45, 14.99),
Pizza('Marinara', 35, 16.99),
]
if __name__ == '__main__':
print(MENU)
# pizza.py
import math
class Pizza:
name: str = ''
size: int = 0
price: float = 0
def __init__(self, name: str, size: int, price: float) -> None:
self.name = name
self.size = size
self.price = price
def area(self) -> float:
return math.pi * math.pow(self.size / 2, 2)
def awesomeness(self) -> int:
if self.name == 'Carbonara':
return 9000
return self.size // int(self.price) * 100
print('pizza.py module name is %s' % __name__)
if __name__ == '__main__':
print('Carbonara is the most awesome pizza.')
Now when I call the menu.py from command like it works as expected.
pizza-shop$ python3 pizzapy/menu.py
pizza.py module name is pizza
[, ,
]
But it fails in REPL:
pizza-shop$ python3
Python 3.7.3 (default, Mar 27 2019, 09:23:15)
[Clang 10.0.1 (clang-1001.0.46.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from pizzapy import menu
Traceback (most recent call last):
File "", line 1, in
File "/Users/aruprakshit/python_playground/pizza-shop/pizzapy/menu.py", line
2, in
from pizza import Pizza
ModuleNotFoundError: No module named 'pizza'
>>>
What is the reason of this inconsistency ?
Thanks,
Arup Rakshit
a...@zeit.io
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[Tutor] help with colormode
hi
Ihave a very small program. I want to cycle colours. I cant set the colormode
from 1 to 255
tried screen.colormode(255)
tells me screen is not defined. the program works without the colormode, but i
want to use it.
I just change the a and b variable values to generate new art.
-code-
from turtle import Turtle
t = Turtle()
t.speed(0)
b = 180
a = 35
colormode(255)
t.color((55,55,55))
for i in range(200):
t.circle(i,a)
t.right(b)
t.circle(i,a)
#input('Press any key to continue...')
-
===error===
Traceback (most recent call last):
File "H:\python\snowflake.py", line 9, in
screen.colormode(255)
NameError: name 'screen' is not defined
===
any help would be appreciated,
thanks
Mark
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Re: [Tutor] help with colormode
Mark Alderson wrote:
> hi
>
> Ihave a very small program. I want to cycle colours. I cant set the
> colormode from 1 to 255
>
> tried screen.colormode(255)
>
> tells me screen is not defined. the program works without the colormode,
> but i want to use it.
>
> I just change the a and b variable values to generate new art.
>
> -code-
> from turtle import Turtle
> t = Turtle()
> t.speed(0)
>
> b = 180
>
> a = 35
>
> colormode(255)
>
> t.color((55,55,55))
> for i in range(200):
> t.circle(i,a)
> t.right(b)
> t.circle(i,a)
>
>
> #input('Press any key to continue...')
>
> -
>
> ===error===
> Traceback (most recent call last):
> File "H:\python\snowflake.py", line 9, in
> screen.colormode(255)
> NameError: name 'screen' is not defined
> ===
The only name you import is Turtle, so you only have that (and the built-
ins). Fortunately you can get the screen from the Turtle, so:
from turtle import Turtle
ninja = Turtle()
ninja.speed(0)
screen = ninja.screen
screen.colormode(255)
b = 180
a = 35
for i in range(200):
ninja.color((i + 55, 55, 55))
ninja.circle(i, a)
ninja.right(b)
ninja.circle(i, a)
screen.exitonclick()
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[Tutor] str.replace error
I'm working wtih python 3.7 on Windows 10.
I'm trying to write some code in order to clean up the data in the csv file.
Using spreadsheet language, I want to replace part of a cell ("Basic P1")
with an empty string and write it in the comments cell.
I thought assigning a variable and replacing the string would be a good
idea.
Here is my code:
import csv
with open('somefile') as csvDataFile:
csvReader = csv.reader(csvDataFile)
for row in range(100):
a = "Basic P1"
str.replace(a, "")
print(next(csvReader))
I get an error:
Traceback (most recent call last):
File "somefile", line 7, in
str.replace(a, "")
TypeError: replace() takes at least 2 arguments (1 given)
But I think I have 2 arguments: a being the "old" argument as per the
documentation, "" being the "new" argument as per the documentation.
What am I missing?
--
Roger Lea Scherer
623.255.7719
*Strengths:*
Input, Strategic,
Responsibility,
Learner, Ideation
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Re: [Tutor] help with colormode
On 25/04/2019 11:54, Mark Alderson wrote:
> tried screen.colormode(255)
Peter has shown you how to make that work but
there is a wee issue below I need to point out.
> -code-
> from turtle import Turtle
> t = Turtle()
> t.speed(0)
>
> b = 180
> a = 35
>
> colormode(255)
>
> t.color((55,55,55))
> for i in range(200):
> t.circle(i,a)
> t.right(b)
> t.circle(i,a)
>
>
> #input('Press any key to continue...')
>
> -
>
> ===error===
> Traceback (most recent call last):
> File "H:\python\snowflake.py", line 9, in
> screen.colormode(255)
> NameError: name 'screen' is not defined
> ===
The error message clearly does not reflect the code above.
In this case its not too bad but in more complex questions
it is very important that you send the actual code that
generates the error. Otherwise we wind up just guessing
at what might be the problem.
Just something for future reference.
Regards from Stirling,
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] str.replace error
On 25/04/2019 18:46, Roger Lea Scherer wrote:
> Here is my code:
>
> import csv
>
> with open('somefile') as csvDataFile:
> csvReader = csv.reader(csvDataFile)
> for row in range(100):
what happens if there are more rows in the file than 100?
Or even if there are less!?
> a = "Basic P1"
> str.replace(a, "")
where does str come from? You haven't assigned anything
to str, this is the first mention.
did you mean to do something like
for str in csvreader:
?
> print(next(csvReader))
>
> I get an error:
>
> Traceback (most recent call last):
> File "somefile", line 7, in
> str.replace(a, "")
> TypeError: replace() takes at least 2 arguments (1 given)
I would expect a name error. So I think the code you
sent is not the code that generated the error. But
without the original code we have no idea what str
actually is.
If it is some kind of string remember that Python strings
are immutable so to get the changed string you need
to store the result. Possibly something like:
str = str.replace(...)
> But I think I have 2 arguments: a being the "old" argument as per the
> documentation, "" being the "new" argument as per the documentation.
>
> What am I missing?
We can't say because we can't see the code that produced the error.
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] str.replace error
On Thu, Apr 25, 2019 at 10:46:31AM -0700, Roger Lea Scherer wrote:
> with open('somefile') as csvDataFile:
> csvReader = csv.reader(csvDataFile)
> for row in range(100):
> a = "Basic P1"
> str.replace(a, "")
> print(next(csvReader))
I'm not quite sure what you expected this to do, but you've
(deliberately? accidently?) run into one of the slightly advanced
corners of Python: unbound methods. Apologies in advance, but this may
be a bit technical. For a suggestion on how to fix the problem, see
right at the end.
Normally when you call a string method, you do something like this:
mystring = "Something here"
newstring = mystring.replace("here", "there")
The technical name for the mystring.replace call is a "bound method", as
the method is "bound" to a string instance (mystring). The method
actually takes *three* arguments: the string to operate on, the
substring to be replaced, and the replacement string:
(string to operate on) . replace ( substring to be replaced, replacement )
But under the hood, what that turns into is an "unbound method" that
calls the method attached to the *class* "str":
str.replace(string to operate on, substring to replace, replacement)
Alas, when you call an *unbound* method like this:
str.replace(a, "")
the interpreter may get a bit confused and report a slightly inaccurate
error message:
> TypeError: replace() takes at least 2 arguments (1 given)
For technical reasons, all the counts are off by one. The error message
should say:
TypeError: replace() takes at least 3 arguments (2 given)
but because the same error message gets used for both bound and unbound
methods, the counts are off for unbound methods. This is an annoyance,
but given that unbound methods are relatively rare, not a large one.
So how do you fix your code?
(1) First of all, you need a string to operate on. I'm not sure which
string that should be -- do you want to check *every* cell? Just the
first cell in each row? Every second row? That's up to you to decide.
(2) Secondly, strings in Python are "immutable" -- that is to say, they
cannot be changed in place. Unlike languages like (say) Pascal, if you
want to change the value of a string, you need to re-assign a new
string:
a = "Hello World!"
a.upper() # Doesn't work!!!
print(a) # Still gives "Hello World!"
Instead you need to say a = a.upper().
(3) Unbound methods are a slightly advanced technique which you don't
need here, so you should just use normal method call.
Putting those three changes together gives something like this:
with open('somefile') as csvDataFile:
csvReader = csv.reader(csvDataFile)
for row in range(100): # How do you know there are only 100 rows?
mystring = "Something here? ~Basic P1~ but I don't know what"
print("Before:", mystring)
mystring = mystring.replace("Basic P1", "")
print("After:", mystring)
print(next(csvReader))
Hopefully that's enough to set you on the right track. If not, please
feel free to write back to the list and ask more questions!
--
Steven
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Re: [Tutor] module import from a packager works inconsistent between REPL and command line
On Thu, Apr 25, 2019 at 05:40:18PM +0530, Arup Rakshit wrote: > I have a small app like this: Please simplify your code to the minimum needed to demonstrate the problem you are asking about. This bit is excellent: > pizza-shop$ tree . > . > └── pizzapy > ├── __init__.py > ├── menu.py > └── pizza.py > > 1 directory, 3 files Nicely shown! But we don't need to see all the gory details of menu.py and especially not of pizza.py, all those methods in pizza.Pizza are irrelevant to the problem. Please read this: http://www.sscce.org/ for a guide. It is written for Java programmers, but it applies to any language. All we need in menu.py is a single line: # menu.py from pizza import Pizza because that's the line that fails. And for pizza.py, all we need is: # pizza.py Pizza = None > Now when I call the menu.py from command like it works as expected. When you ask Python to import a module, it doesn't search the entire hard drive, that could take hours if the drive is big enough. It only looks in the search-path. At runtime, you can see the paths searched like this: import sys print(sys.path) which will show you where Python is looking for modules. When you directly call a module: python path/to/menu.py the directory holding that module is included in the search path, so if you also have path/to/pizza.py the "import pizza" will work. But in the REPL, only the default search path is used. In your case, the fix is, I think, to change menu.py to do this: # was: from pizza import Pizza from pizzapy.pizza import Pizza which I *think* will solve the problem, but I haven't tested it. For what it is worth, importing problems are sometimes annoying to solve. What works as a good design for importing libraries doesn't always make a good design for scripts that you call directly from the command line, and visa versa, so the import system is a bit of a compromise between the two. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] When you think to setup the __class__ of a module object to a subclass of ModuleType
On Thu, Apr 25, 2019 at 02:52:07PM +0530, Arup Rakshit wrote: > Here it is: *3.3.2.1. Customizing module attribute access* > (https://docs.python.org/3/reference/datamodel.html#customizing-module-attribute-access) Oh! That's brand new in 3.7, no wonder I didn't know about it. I did see the core developers talking about adding this feature, but I didn't know that they had done so. Your original question was: > In the simple code like what are the advantages we get from? Is this > so that we can implement more special methods than just __getattr__ > and __dir__ in the module level? Yes, that's what the documentation says. I don't see any reason not to believe it. Oh, this is cool! I'm going to enjoy playing with this... py> from types import ModuleType py> class Magic(ModuleType): ... count = 0 ... @property ... def spam(self): ... self.count += 1 ... return ' '.join(['spam']*self.count) ... py> import sys py> sys.modules['__main__'].__class__ = Magic py> import __main__ py> __main__.spam 'spam' py> __main__.spam 'spam spam' py> __main__.spam 'spam spam spam' -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
