FAQ
How can one check that a Python script is lexically correct?

As my Python apps grow in complexity and execution, I'm finding it
more often the situation in which a program dies after a lengthy
(i.e. expensive) run because the execution reaches, say, a typo.
Of course, this typo needs to be fixed, but I'd like to find out
about it before I waste hours on a run that is bound to fail. Is
there any way to do this? I imagine the answer is no, because
given Python's scoping rules, the interpreter can't know about
these things at compile time, but I thought I'd ask.

TIA!

kynn

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  • Daniel da Silva at Oct 29, 2009 at 8:56 pm
    There are several static analysis tools that can check whether a variable
    name is used before it is defined.

    At my old workplace we used "pylint", so I can recommend that:
    http://www.logilab.org/857

    --Daniel
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  • Mick Krippendorf at Oct 29, 2009 at 8:57 pm

    kj wrote:
    How can one check that a Python script is lexically correct?
    By using pylint.

    Mick.
  • Diez B. Roggisch at Oct 29, 2009 at 8:59 pm

    kj schrieb:
    How can one check that a Python script is lexically correct?

    As my Python apps grow in complexity and execution, I'm finding it
    more often the situation in which a program dies after a lengthy
    (i.e. expensive) run because the execution reaches, say, a typo.
    Of course, this typo needs to be fixed, but I'd like to find out
    about it before I waste hours on a run that is bound to fail. Is
    there any way to do this? I imagine the answer is no, because
    given Python's scoping rules, the interpreter can't know about
    these things at compile time, but I thought I'd ask.
    pylint, pychecker, pydev. Maybe more.

    Diez
  • Robert Kern at Oct 29, 2009 at 9:32 pm

    On 2009-10-29 15:48 PM, kj wrote:
    How can one check that a Python script is lexically correct?

    As my Python apps grow in complexity and execution, I'm finding it
    more often the situation in which a program dies after a lengthy
    (i.e. expensive) run because the execution reaches, say, a typo.
    Of course, this typo needs to be fixed, but I'd like to find out
    about it before I waste hours on a run that is bound to fail. Is
    there any way to do this? I imagine the answer is no, because
    given Python's scoping rules, the interpreter can't know about
    these things at compile time, but I thought I'd ask.
    I like using pyflakes. It catches most of these kinds of typo errors, but is
    much faster than pylint or pychecker. That means I can hook up a key macro to
    run it in my editor so I can use it frequently without hesitation (e.g. in Vim,
    it is my makeprg for Python files).

    It doesn't catch other stupid errors, of course. Try your best to write small,
    simple, quick-to-run tests for each piece of functionality that you are working
    on. Test the methods you've just coded independently of the rest of your code
    using that small test before doing full hours-long runs of the whole program.
    Bonus: you now have a suite of unit tests.

    --
    Robert Kern

    "I have come to believe that the whole world is an enigma, a harmless enigma
    that is made terrible by our own mad attempt to interpret it as though it had
    an underlying truth."
    -- Umberto Eco
  • Aahz at Oct 29, 2009 at 9:52 pm
    In article <mailman.2279.1256851983.2807.python-list at python.org>,
    Robert Kern wrote:
    I like using pyflakes. It catches most of these kinds of typo errors, but is
    much faster than pylint or pychecker.
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    --
    Aahz (aahz at pythoncraft.com) <*> http://www.pythoncraft.com/

    "You could make Eskimos emigrate to the Sahara by vigorously arguing --
    at hundreds of screens' length -- for the wonder, beauty, and utility of
    snow." --PNH to rb in r.a.sf.f
  • Robert Kern at Oct 29, 2009 at 10:27 pm

    On 2009-10-29 16:52 PM, Aahz wrote:
    In article<mailman.2279.1256851983.2807.python-list at python.org>,
    Robert Kernwrote:
    I like using pyflakes. It catches most of these kinds of typo errors, but is
    much faster than pylint or pychecker.
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    I consider "import *" the first error to be fixed, so it doesn't bother me much. :-)

    --
    Robert Kern

    "I have come to believe that the whole world is an enigma, a harmless enigma
    that is made terrible by our own mad attempt to interpret it as though it had
    an underlying truth."
    -- Umberto Eco
  • Albert Hopkins at Oct 30, 2009 at 12:10 am

    On Thu, 2009-10-29 at 17:27 -0500, Robert Kern wrote:
    I consider "import *" the first error to be fixed, so it doesn't
    bother me much. :-)
    But does pyflakes at least *warn* about the use of "import *" (I've
    never used it so just asking)?
  • Ben Finney at Oct 30, 2009 at 12:19 am

    Albert Hopkins <marduk at letterboxes.org> writes:
    On Thu, 2009-10-29 at 17:27 -0500, Robert Kern wrote:
    I consider "import *" the first error to be fixed, so it doesn't
    bother me much. :-)
    But does pyflakes at least *warn* about the use of "import *" (I've
    never used it so just asking)?
    That's easy enough to check:

    =====
    $ cat namespace_clobber.py
    from foo import *

    $ pyflakes namespace_clobber.py
    namespace_clobber.py:1: 'from foo import *' used; unable to detect undefined names
    =====

    --
    \ ?There are no significant bugs in our released software that |
    `\ any significant number of users want fixed.? ?Bill Gates, |
    _o__) 1995-10-23 |
    Ben Finney
  • Exarkun at Oct 29, 2009 at 10:58 pm

    On 09:52 pm, aahz at pythoncraft.com wrote:
    In article <mailman.2279.1256851983.2807.python-list at python.org>,
    Robert Kern wrote:
    I like using pyflakes. It catches most of these kinds of typo errors,
    but is
    much faster than pylint or pychecker.
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    Consider it (some very small, I'm sure) motivation to stop using "import
    *", which is itself only something used in unimpressive software. ;)

    Jean-Paul
  • Ben Finney at Oct 29, 2009 at 11:25 pm

    aahz at pythoncraft.com (Aahz) writes:

    Coincidentally, I tried PyFlakes yesterday and was unimpressed with
    the way it doesn't work with "import *".
    That's pretty much the reason to avoid ?from foo import *?: it makes the
    namespace indeterminate without actually running the code. Just as much
    a problem for the human reader as for a reader like ?pyflakes?.

    But you knew that already.

    --
    \ ?Humanity has advanced, when it has advanced, not because it |
    `\ has been sober, responsible, and cautious, but because it has |
    _o__) been playful, rebellious, and immature.? ?Tom Robbins |
    Ben Finney
  • Bruno Desthuilliers at Oct 30, 2009 at 8:53 am

    Robert Kern a ?crit :
    On 2009-10-29 16:52 PM, Aahz wrote:
    (snip)
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    I consider "import *" the first error to be fixed, so it doesn't bother
    me much. :-)
    +1 QOTW
  • Singletoned at Nov 3, 2009 at 12:53 pm

    On Oct 30, 8:53?am, Bruno Desthuilliers <bruno. 42.desthuilli... at websiteburo.invalid> wrote:
    Robert Kern a ?crit :> On 2009-10-29 16:52 PM, Aahz wrote:
    (snip)
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    I consider "import *" the first error to be fixed, so it doesn't bother
    me much. :-)
    +1 QOTW
    Bruno, do you actually get to decide the QOTW? Because everytime you `
    +1 QOTW` it gets to be the QOTW.

    Ed

    BTW I was the grateful recipient of your vote the other week.
  • Lie Ryan at Oct 30, 2009 at 1:32 pm

    Aahz wrote:
    In article <mailman.2279.1256851983.2807.python-list at python.org>,
    Robert Kern wrote:
    I like using pyflakes. It catches most of these kinds of typo errors, but is
    much faster than pylint or pychecker.
    Coincidentally, I tried PyFlakes yesterday and was unimpressed with the
    way it doesn't work with "import *".
    If only IDLE's Intellisense worked without having to run the code first,
    perhaps I wouldn't have abandoned using IDE altogether to write codes
    and used vim/gedit/notepad/whateverpad instead. I've felt liberlized
    since going plaintext.
  • Alex23 at Oct 30, 2009 at 3:19 am

    kj wrote:
    As my Python apps grow in complexity and execution, I'm finding it
    more often the situation in which a program dies after a lengthy
    (i.e. expensive) run because the execution reaches, say, a typo.
    This is a good reason for breaking your program down into testable
    units and verifying they behave as expected before a long execution
    phase. You can get a long way with unittest in the stdlib, but I
    personally prefer using nose[1], I find the tests to be less weighty
    in boilerplate.

    1: http://code.google.com/p/python-nose/
  • Fabio Zadrozny at Oct 30, 2009 at 8:02 pm

    On Thu, Oct 29, 2009 at 6:48 PM, kj wrote:
    How can one check that a Python script is lexically correct?

    As my Python apps grow in complexity and execution, I'm finding it
    more often the situation in which a program dies after a lengthy
    (i.e. expensive) run because the execution reaches, say, a typo.
    Of course, this typo needs to be fixed, but I'd like to find out
    about it before I waste hours on a run that is bound to fail. ?Is
    there any way to do this? ?I imagine the answer is no, because
    given Python's scoping rules, the interpreter can't know about
    these things at compile time, but I thought I'd ask.
    Pydev has a code-analysis feature which works analyzing the code while
    you're typing. See: http://pydev.org/manual_adv_code_analysis.html

    Cheers,

    Fabio
  • Alan Franzoni at Oct 31, 2009 at 11:39 am

    On 10/29/09 9:48 PM, kj wrote:
    How can one check that a Python script is lexically correct?
    You can use a pseudo-static analyzer like pyflakes, pylint or pydoctor.

    Or, better, you can avoid wild imports, excessive local or global
    namespace manipulation, and break you program in smaller parts and write
    unit tests for them.

    Typos are very common but should very easy to catch. If you're not
    catching them until a very long run of your program, then your code
    coverage is probably too low.

    --
    Alan Franzoni
    contact me at public@[mysurname].eu

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postedOct 29, '09 at 8:48p
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