How can I find all placeholders for str.format in a python string using a regex? [duplicate]

I'm creating a class that renames a file using a user-specified format. This format will be a simple string whose str.format method will be called to fill in the blanks.

It turns out that my procedure will require extracting variable names contained in braces. For example, a string may contain {user}, which should yield user. Of course, there will be several sets of braces in a single string, and I'll need to get the contents of each, in the order in which they appear and output them to a list.

Thus, "{foo}{bar}" should yield ['foo', 'bar'].

I suspect that the easiest way to do this is to use re.split, but I know nothing about regular expressions. Can someone help me out?

Thanks in advance!

Solution 1:

Another possibility is to use Python's actual Formatter itself to extract the field names for you:

>>> import string
>>> s = "{foo} spam eggs {bar}"
>>> string.Formatter().parse(s)
<formatteriterator object at 0x101d17b98>
>>> list(string.Formatter().parse(s))
[('', 'foo', '', None), (' spam eggs ', 'bar', '', None)]
>>> field_names = [name for text, name, spec, conv in string.Formatter().parse(s)]
>>> field_names
['foo', 'bar']

or (shorter but less informative):

>>> field_names = [v[1] for v in string.Formatter().parse(s)]
>>> field_names
['foo', 'bar']

Solution 2:

Using re.findall():

In [5]: import re

In [8]: strs = "{foo} spam eggs {bar}"

In [9]: re.findall(r"{(\w+)}", strs)
Out[9]: ['foo', 'bar']