[Python-ideas] Adding '**' recursive search to glob.glob

[Steven D'Aprano]

On 15/01/13 02:46, Vinay Sajip wrote:
> Paul Moore<p.f.moore at ...>  writes:
>
>> I'd like it if the glob module supported the (relatively common)
>> facility to use ** to mean recursively search subdirectories.

+1

>> One obvious downside is that if used carelessly, it can make globbing
>> pretty slow. So I'd propose that it be added as an optional extension
>> enabled using a flag argument (glob(pat, allow_recursive=True)) which
>> is false by default. That would also mean that backward compatibility
>> should not be an issue.
>
> Isn't the requirement to recurse implied by the presence of '**' in the
> pattern? What's to be gained by specifying it using allow_recursive as well?

Not necessarily. At the moment, a glob like "/**/spam" is equivalent to
"/*/spam":


[steve at ando /]$ touch /tmp/spam
[steve at ando /]$ mkdir /tmp/ham
[steve at ando /]$ touch /tmp/ham/spam
[steve at ando /]$ python3.3 -c "import glob; print(glob.glob('/**/spam'))"
['/tmp/spam']


With the suggested new functionality, the meaning of the glob will change.

 From a backwards-compatibility point of view, one might not want to enable
the new semantics by default. But, from a *future*-compatibility point of
view, I don't know that it is a good idea to require a flag every time a
new globbing feature is added.

glob.glob(pattern, allow_recurse=True, allow_spam=True, allow_ham=True, allow_eggs=True, ...)


Rather than a flag, I suggest a version number:

glob.glob(pattern, version=1)  # current behaviour, as of 3.3
glob.glob(pattern, version=2)  # adds ** recursion in Python 3.4

Then in Python 3.5 or 3.6 support for version 1 globs could be dropped.



> Will having allow_recursive=True have any effect if '**' is not in the
> pattern?

I would expect that it will not have any effect unless ** is present.
After all, it simply allows ** to recurse, and no other glob
metacharacter can recurse.


>If you specify a pattern with '**' and allow_recursive=False, does
> that mean that '**' effectively acts as '*' would (i.e. one directory level
> only)?

I expect that without allow_recursive=True, ** would behave identically to
a single *


-- 
Steven