possible false positive E303

[dimaqq]

Consider following valid code, at module top level:

# snip
class Foo:
    pass

class Bar:
    pass
# snip

Consider making it conditional, at module top level:

# snip
if something:
    class Foo:
        pass

    class Bar:
        pass
# snip

pep8 reports E303 too many blank lines (2) before Bar in the conditional case. semantically it is a false positive. syntactically it is an unclear case.

from PEP 8: Separate top-level function and class definitions with two blank lines. Method definitions inside a class are separated by a single blank line. Extra blank lines blah blah blah...

this particular case doesn't fall in either clearly defined category.

[florentx]

I agree that it is in the gray area.

I did not receive any criticism for this behavior before, and it seems acceptable to me.

However it is open for discussion.

[garyd203]

An alternate point of view is that code like the above is more like a script than a standalone module (since it is not just a collection of definitions). If this distinction is meaningful, then we could treat this situation like code inside a function, and hence require a single blank line to separate logically distinct sections.

That said, this particular situation feels like it should be valid. However, that is more of a subjective judgment than something that I can describe in an algorithm.

[chrismedrela]

Does anybody use conditional classes? I wonder if this issue is a real problem. If not, this ticket could be closed.

[garyd203]

This situation applies to top-level functions, in addition to classes.

I have seen conditional functions used as a technique to provide OS-dependent implementations. For example, the urllib module in Python 2.7 has:

if sys.platform == 'darwin':
    ...
    def proxy_bypass(host):
        ...

    def getproxies():
        ...

elif os.name == 'nt':
    ...
    def proxy_bypass(host):
        ...

    def getproxies():
        ...

Granted, there are other (perhaps better) ways to achieve this, but nonetheless it is a real technique.

[jayvdb]

I inherited a bunch of conditional classes, which was a OS-dependent implementation as suggested by garyd203 , and were basically this recipe:

http://stackoverflow.com/questions/878972/windows-cmd-encoding-change-causes-python-crash/3259271#3259271

The fix was not to worry about pep8's limitations, but completely overhaul it to move the classes to the top-level. https://gerrit.wikimedia.org/r/#/c/239540/3/pywikibot/userinterfaces/win32_unicode.py,cm

[IanLee1521]

Closing as I feel that since it doesn't fall into either of the "two line separation" cases, this should be handled with a single line of indentation between the classes. If there is a strong opinion, I would recommend reaching out to the python-dev list to try to get the PEP-8 document updated to clarify this case.