Parameterized Regular Expression in Python

Question

In Python, there is a better way for strings to parameterize strings in regular expressions than to do it manually:

test = 'flobalob'
names = ['a', 'b', 'c']
for name in names:
    regexp = "%s" % (name)
    print regexp, re.search(regexp, test)

This noddy example tries to match each name in turn. I know that it’s better to do this, but this is a simple example to illustrate this point.

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The answer seems no, there is no real alternative. The best way to parameterize regular expressions in python is as above, or with derivatives like str.format(). I tried to write a general question, not "fix ma codez, thank you". For those who are interested, I gave an example that is closer to my needs:

for diskfilename in os.listdir(''):
    filenames = ['bob.txt', 'fred.txt', 'paul.txt']
    for filename in filenames:
        name, ext = filename.split('.')
        regexp = "%s.*\.%s" % (name, ext)
        m = re.search(regexp, diskfilename)
        if m:
          print diskfilename, regexp, re.search(regexp, diskfilename)
          # ...

"" <filename>_<date>.<extension>. filenames - dict, , .

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, . . fnmatch, .

Answer 1

, , . :

d = {'bar': 'a', 'foo': 'b'}
regexp = '%(foo)s|%(bar)s' % d

, , :

vlist = ['a', 'b', 'c']
regexp = '|'.join([s for s in vlist])

EDIT: , , .

, , :

filename = 'bob_20090216.txt'

regexps = {'bob': 'bob_[0-9]+.txt',
           'fred': 'fred_[0-9]+.txt',
           'paul': 'paul_[0-9]+.txt'}

for filetype, regexp in regexps.items():
    m = re.match(regexp, filename)
    if m != None:
        print '%s is of type %s' % (filename, filetype)

Answer 2

import fnmatch, os

filenames = ['bob.txt', 'fred.txt', 'paul.txt']

                  # 'b.txt.b' -> 'b.txt*.b'
filepatterns = ((f, '*'.join(os.path.splitext(f))) for f in filenames) 
diskfilenames = filter(os.path.isfile, os.listdir(''))
pattern2filenames = dict((fn, fnmatch.filter(diskfilenames, pat))
                         for fn, pat in filepatterns)

print pattern2filenames

:

{'bob.txt': ['bob20090217.txt'], 'paul.txt': [], 'fred.txt': []}

:

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, filename.startswith(prefix) .

, , .

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• re.escape(name), name.

• , . :

  import string
  print string.Template("$a $b").substitute(a=1, b="B")
  # 1 B
  

  str.format() Python 2.6 +:

  print "{0.imag}".format(1j+2)
  # 1.0
  

Answer 3

maybe glob and fnmatch can help you?