Re: repr = expression representation?
Am 17.05.19 um 06:13 schrieb Stefan Ram: However, look at this |>>> print( str( print )) | |>>> print( repr( print )) | . While it is nice that »str( print )« gives some useful information, I would expect »repr( print )« to give »print« - This is impossible. Python does not use "call by name", so a function cannot know how the argument is called in the upper stack level. Consider: Apfelkiste:inotes chris$ python3 Python 3.6.1 |Anaconda 4.4.0 (x86_64)| (default, May 11 2017, 13:04:09) [GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> blafasel = print >>> print(repr(blafasel)) >>> You'll have to accept that not all Python objects can be represented as literals. While a user defined function /could/ be printed as a lambda, so expecting: def test(x): return 2*x print(repr(test)) -> lambda x : 2*x would be half-reasonable, it is impossible to print out the C source code of the built-in print function, unless one builds a JIT C compiler into Python. Christian -- https://mail.python.org/mailman/listinfo/python-list
EuroPython 2019: Sponsor brochure available
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Re: How to read barcoded value from PDF
在 2011年6月28日星期二 UTC+8下午5:30:21，Robin Becker写道：
> On 28/06/2011 06:59, Asif Jamadar wrote:
> > Hi,
> >
> ...
> >
> > In Reportlab I can do the following code to generate barcode and to get the
> > value of that barcode
> >
> >
> >
> >
> > barcode=code39.Extended39("123456789",barWidth=0.2*mm,barHeight=8*mm)
> >
> >
> >
> > bc = Paragraph("Barcode value: %s" % barcode.value,
> > STYLES['Normal'])
> >
> >
> >
> > document.append(bc)
> >
> > But how can I achieve this from the existing PDF document??
> .
>
> you might consider asking on the reportlab list as there is considerable
> experience there about pdf in general.
>
> It's unlikely that you will be able to easily discern which string/text in
> the
> pdf corresponds to the barcode values that you are interested in.
>
> PDF does allow things called annotations which reportlab can generate.
>
> Alternatively you can generate an invisible string which may make more sense
> than the simple barcode value. So when you draw the barcode you also need to
> add
> the magic string using some prefix/postfix that allows easy extraction with
> pypdf or similar eg
>
> "===radamajfisa===123456789===radamajfisa===". Your text extractor should be
> able to find this without too much trouble.
> --
> Robin Becker
You can check out this .net barcode reader for PDF document:
http://www.barcodec.com/products/netpdfbarcodereader-all.html. It might be
helpful.
--
https://mail.python.org/mailman/listinfo/python-list
Re: repr = expression representation?
Christian Gollwitzer writes: > Am 17.05.19 um 06:13 schrieb Stefan Ram: However, look at this >> >> |>>> print( str( print )) >> | >> >> |>>> print( repr( print )) >> | >> >>. While it is nice that »str( print )« gives some useful >>information, I would expect »repr( print )« to give >>»print« - > > This is impossible. Python does not use "call by name", so a function > cannot know how the argument is called in the upper stack > level. Consider: > > Apfelkiste:inotes chris$ python3 > Python 3.6.1 |Anaconda 4.4.0 (x86_64)| (default, May 11 2017, 13:04:09) > [GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin > Type "help", "copyright", "credits" or "license" for more information. blafasel = print print(repr(blafasel)) > I don't think that renaming is important to SR. The result should be, in his view, a string representing the /value/ of the argument to repr, so repr(print) and replr(blafasel) could both return the same (as they indeed do) thing and I think he'd be happy. > You'll have to accept that not all Python objects can be represented > as literals. I don't think SR minds if the result is not a literal. I think the hope was simply that eval(repr(E)) === E for any expression E. You could, in a very limited way, fudge it like this: def myrepr(e): if isinstance(e, types.BuiltinFunctionType): return e.__name__ return repr(e) The trouble is that print does not always mean print because that identifier can be rebound. Python could try to provide some /other/ name for every object, one that can't be rebound (something like an environment + string lookup) but it's probably not worth it. -- Ben. -- https://mail.python.org/mailman/listinfo/python-list
About: Python not recognizing command even after installed Python 3.7.3
Dear Team I have already installed python 3.7.3 64-bit in my window 8.1. I started learning Django using python. But after few days 4-5 days I found python not recognizing command. Could you please advise me. Is there any possibilities of Antivirous update and running for removing virous . Thanks Regards Jai Prakash -- https://mail.python.org/mailman/listinfo/python-list
Re: Import module from a different subdirectory
On Fri, 17 May 2019, Inada Naoki wrote: This is slightly off topic (not relating to your problem), but please don't think "Python 3 doesn't require __init__.py for packages". It is common misunderstanding. Inada, Actually, your response is on topic and probably the reason I have the import problem. Package directory without __init__.py is "namespace package". Namespace package is not a regular package. See [1] for detail. Thank you for correcting me. Regards, Rich -- https://mail.python.org/mailman/listinfo/python-list
Re: Import module from a different subdirectory
On Thu, 16 May 2019, Rich Shepard wrote: The project directory contains subdirectories, including gui/ (with the tkinter views) and classes/ with the SQLAlchemy model.py. Getting closer, but still missing a piece of the solution. First, I added __init__.py to each module subdirectory to specify that the subdirectory is a package. Second, in ~/.bash_profile I added two lines, the first is the project's root directory: PYTHONPATH=$HOME/development/bustrac export PYTHONPATH Testing this suggests that python is finding the path: $ python3 Python 3.7.3 (default, Mar 26 2019, 06:40:28) [GCC 5.5.0] on linux Type "help", "copyright", "credits" or "license" for more information. import os os.environ["PYTHONPATH"] '/home/rshepard/development/bustrac' but the import is still not working. Do I need to specify each bustrac/ subdirectory in the PYTHONPATH? If not, what am I still missing? Regards, Rich -- https://mail.python.org/mailman/listinfo/python-list
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Re: Instance vs Class variable oddity
> On May 15, 2019, at 5:41 PM, Ben Finney wrote: > > Irv Kalb writes: > >> I just saw some code that confused me. The confusion has to do with >> class variables and instance variables. > > (Perhaps unrelated, but here's another confusion you may be suffering > from: There's no such thing as a “class variable” or “instance > variable”. In Python, a “variable” is always a *binding* between a name > and and object. The “variable” has no concept of different types.) > >> > > I'm not sure I understand the confusion; once the instance has an > attribute of that name, the same logic you outlined above applies when > attempting to resolve that attribute. When ‘self.x’ exists on the > instance, that's what will be used when resolving ‘self.x’. > > I hope that helps. > Thanks for your comments. I am very aware of all the other issues that you explained. The only thing that threw me was that in a line like: self.x = self.x + 1 in a method, these two uses of self.x can refer to different variables. I actually teach Python, and this would be a very difficult thing to explain to students. I have never run across this issue because I would never use the same name as an instance attribute and a class attribute. (I also know that "attribute" is the "official" terms, but I've called them instance variables and class variables for so many years (working in other languages), that I use those terms without thinking.) Thanks, Irv -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance vs Class variable oddity
On Sat, May 18, 2019 at 4:40 AM Irv Kalb wrote: > > Thanks for your comments. I am very aware of all the other issues that you > explained. > > The only thing that threw me was that in a line like: > > self.x = self.x + 1 > > in a method, these two uses of self.x can refer to different variables. I > actually teach Python, and this would be a very difficult thing to explain to > students. > > I have never run across this issue because I would never use the same name as > an instance attribute and a class attribute. (I also know that "attribute" > is the "official" terms, but I've called them instance variables and class > variables for so many years (working in other languages), that I use those > terms without thinking.) > Yes, this is a little unusual. It's a consequence of the run-time-lookup that defines attributes, as opposed to the compile-time-lookup that defines most name bindings. For instance: x = 0 def f(): print(x) x = 1 print(x) will raise UnboundLocalError, rather than printing zero followed by one. But the global and builtin namespaces are looked up completely dynamically: class int(int): pass This will look up the built-in "int" type, create a subclass, and make that a global. So this is uncommon, but not unique. Sometimes, if one thing doesn't exist, you find another - even if it's going to exist a moment later. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance vs Class variable oddity
On 05/17/2019 11:37 AM, Irv Kalb wrote: self.x = self.x + 1 I have never run across this issue because I would never use the same name as an instance attribute and a class attribute. So you treat your class attributes as if they were static? -- ~Ethan~ -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance vs Class variable oddity
Correct me if I am wrong, please. I always think that the LEGB rule (e.g. the namespace to look up for) was applied at compile-time, only the binding was resolved "dynamically" at run-time. For example: def foo(): print(x) foo() will cause a NameError. But after x = 5 foo() will run correctly. I also don't think the term "variable" and "attribute" can be used exchangeable. Variable apply to an unbound name, and attribute applies to bounded name. For example: foo.x = 3 will create an attribute x of function foo. It's either not a local variable, or a global variable. It's more likely a class instance attribute, and it's resolved by applying MRO rule dynamically. --Jach -- https://mail.python.org/mailman/listinfo/python-list
Re: Import module from a different subdirectory
Rich Shepard writes: >> The project directory contains subdirectories, including gui/ (with the >> tkinter views) and classes/ with the SQLAlchemy model.py. > ... > Second, in ~/.bash_profile I added two lines, the first is the project's > root directory: > > PYTHONPATH=$HOME/development/bustrac > export PYTHONPATH > > Testing this suggests that python is finding the path: > > $ python3 > Python 3.7.3 (default, Mar 26 2019, 06:40:28) [GCC 5.5.0] on linux > Type "help", "copyright", "credits" or "license" for more information. import os os.environ["PYTHONPATH"] > '/home/rshepard/development/bustrac' Test this by looking at "sys.path" instead: >>> import sys >>> sys.path It is "sys.path" which actually controls the import machinery. > ... > Do I need to specify each bustrac/ subdirectory in the PYTHONPATH? If not, > what am I still missing? This depends on how you make the import. "sys.path" is typically a sequence of folders. Python's import machinery will look in those folders for modules/paackages for its (absolute) imports. Thus, if you use "import " or "from import ...", then one of those folders should contain a module or package named "". -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance vs Class variable oddity
Irv Kalb writes: > ... > The only thing that threw me was that in a line like: > > self.x = self.x + 1 > > in a method, these two uses of self.x can refer to different variables. I > actually teach Python, and this would be a very difficult thing to explain to > students. > > I have never run across this issue because I would never use the same name as > an instance attribute and a class attribute. I use this regularly. Think of the "class attribute" as providing a default for a potential "instance attribute" of the same name. In Python, almost everything from a class can be overridden by the instance (exceptions: some special methods, descriptors). Thus, one can (almost) view a class as a defaults provider for its instances. Class attributes are just one case. -- https://mail.python.org/mailman/listinfo/python-list
