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Inconsistencies with tab/space indentation between Cygwin/Win32?

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  Inconsistencies with tab/space indentation between Cygwin/Win32? "Christian Gelinek" <cgelinek@radlogic.com.au> - 2011-08-04 13:55 +0930
    Re: Inconsistencies with tab/space indentation between Cygwin/Win32? Thorsten Kampe <thorsten@thorstenkampe.de> - 2011-08-04 07:18 +0200
    Re: Inconsistencies with tab/space indentation between Cygwin/Win32? Nobody <nobody@nowhere.com> - 2011-08-04 22:35 +0100

#10839 — Inconsistencies with tab/space indentation between Cygwin/Win32?

Hi all,

I have a problem running some python program using version 2.6.4 (or version
2.7.2, I tried both) from the Win7 command line - it never finishes due to
an infinite loop. The thing is, when I run the same program through Cygwin
which uses Python version 2.6.5, it exits the loop at some point.

I came to try this after I realised that in some of the sources (it is a
rather big program using many source files, most of them being created by
others from a Linux environment), the indentation is mixed tabs/spaces where
the assumed tab size is 8 spaces.

Reading on the Python website, a tab size of 8 is default anyway, so I would
have assumed it should work... does that mean that one tab equals 2
indents?!? I myself never use tabs to indent Python code but let my editor
do a tab-to-4-spaces conversion when I press <TAB>.

I find it at least confusing to read that Python expects a tab size of 8 but
at the same time uses 4 spaces for one indent level. Or maybe I am
completely on the wron track here?

Any ideas on how to get the thing to run under (real) Windows, hopefully
without having to edit existing sources of people who left our company ages
ago?

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#10841

* Christian Gelinek (Thu, 4 Aug 2011 13:55:37 +0930)
> Any ideas on how to get the thing to run under (real) Windows,
> hopefully without having to edit existing sources of people who left
> our company ages ago?

python -t
"Issue a warning when a source file mixes tabs and spaces for
indentation in a way that makes it depend on the worth of a tab
expressed in spaces. Issue an error when the option is given twice."

Thorsten

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#10880

On Thu, 04 Aug 2011 13:55:37 +0930, Christian Gelinek wrote:

> I find it at least confusing to read that Python expects a tab size of 8 but
> at the same time uses 4 spaces for one indent level. Or maybe I am
> completely on the wron track here?

4-column indents are a convention, not a rule. You can use however many
columns you like, and you don't even need to be consistent about it; you
can use 2 columns for one "block" and 4 columns for another. Python only
cares about "indented more than the previous line" and "indented to a
depth matching an outer level of the code".

8-column tab stops are a rule, due to it being such a long-standing
convention that some software and hardware has 8-column tab stops
hardwired (and anything which allows tab stops to be configured normally
defaults to 8 columns).

> Any ideas on how to get the thing to run under (real) Windows, hopefully
> without having to edit existing sources of people who left our company ages
> ago?

The only time you'll have problems is if you copy-and-paste code which was
written using a mix of tabs and spaces and which assumed a different tab
width. If code only ever uses tabs, the tab width doesn't matter. If code
uses a mix of tabs and spaces and it actually works, it's correct
according to Python's 8-column tab stops, even if that's not how the
programmer's editor was set up. Also, copying blocks of code which start
and end at the top-level (i.e. without indentation) will work regardless.

Where it fails is if you copy indented code from e.g. a file which used a
mix of spaces and 4-column tabs into a file which uses 8-column tabs.

If you have existing code which uses a mix of tabs and spaces where tabs
aren't 8 columns (or you aren't sure that they're 8 columns), your best
bet is to reformat the code to avoid using tabs (on Unix: "pr -t -e", or
"pr -t -e4" for 4-column tabs).

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