inspect.findsource problem with llinecache

[Rafe]

On Nov 12, 2:22 pm, Rafe <rafesa... at gmail.com> wrote:
> Hi,
>
> I think I have discovered two bugs with the inspect module and I would
> like to know if anyone can spot any traps in my workaround.
>
> I needed a function which takes a function or method and returns the
> code inside it (it also adjusts the indent because I have to paste the
> to a text string without indents, which is parsed later...long story).
> At first this seemed trivial but then I started getting an error on
> line 510 of inspect.py:
> 504    if iscode(object):
> 505        if not hasattr(object, 'co_firstlineno'):
> 506            raise IOError('could not find function definition')
> 507        lnum = object.co_firstlineno - 1
> 508        pat = re.compile(r'^(\s*def\s)|(.*(?<!\w)lambda(:|\s))|^
> (\s*@)')
> 509        while lnum > 0:
> 510            if pat.match(lines[lnum]): break
> 511            lnum = lnum - 1
> 512        return lines, lnum
>
> I finally figured out that there was a caching problem. The function I
> passed was changed, but the code lines (strings) retrieved by
> linecache.getlines() (on lines 464 and 466) didn't update with the new
> module contents. The resulting error I was getting occurred when real
> module had less lines than the cached module (or the other way around,
> whatever.)
>
> To get around this, I invoke linecache.clearcache(). Here is the
> function (minus doc strings)...
>
> INDENT_SPACES = 4
>
> def get_fn_contents(fn, remove_indents=1):
>     # Clear the cache so inspect.getsourcelines doesn't try to
>     # check an older version of the function's module.
>     linecache.clearcache()
>     source_lines, n = inspect.getsourcelines(fn)
>
>     # Skip the first line which contains the function definition.
>     # Only want the code inside the function is needed.
>     fn_contents = source_lines[1:]
>
>     # Remove indents
>     new_indent_lines = [remove_indent(line, remove_indents) for line
> in fn_contents]
>
>     return "".join(new_indent_lines)
>
> def remove_indent(in_str, num_indent=1):
>     s = in_str
>     for i in range(num_indent):
>         if s[:INDENT_SPACES] == "    ":   # Whitespace indents
>             s = s[INDENT_SPACES:]
>         elif s[:1] == "\t":   # Tab characters indents
>              s = s[1:]
>
>     return s
>
> [END CODE]
>
> The second issue is that the last line in the passed function's module
> seems to be ignored. So, if the last line of the module is also the
> last line of the function, the function is returned one line too
> short.
>
> I welcome comments on the bugs or optimization pointers for my code. I
> am still quite new to Python. My primary question though is: will
> linecache.clearcache() cause me any problems?
>
> Thanks,
>
> - Rafe


I forgot to add that while inspect uses the cached module to get the
text, the line number used to find the block of source lines is
retrieved from the passed object. So, if I pass a function which
reports that it starts on line 50, but in the cache it starts on line
40 an error isn't raised but the lines of code returned are wrong. The
error only occurs when the line number is higher than the number of
lines in the cached module.

- Rafe