Python：在使用str.lower时，如何避免使用小写字符串中的特定单词

Question

Iam new to python

i have a list of string as follws

mylist=["$(ProjectDir)Dir1\Dest1","$(OutDir)Dir2\Dest2","$(IntDir)Dir2\Dest2"]

i want to lower case each list item value as follows

mylist=["$(ProjectDir)dir1\dest1","$(OutDir)dir2\dest2","$(IntDir)dir3\dest3"]

ie i want to prevent $(ProjectDir) , $(OutDir) , $(IntDir) from lowercasing

Answer 1

The idea is very simple. You split the string with a regular expression describing parts that are not to be converted, then convert only its even parts, then join them back.

>>> import re
>>> mylist=["$(ProjectDir)Dir1\Dest1","$(OutDir)Dir2\Dest2","$(IntDir)Dir2\Dest2"]
>>> print ["".join([s if i%2 else s.lower()  for (i,s) in enumerate(re.split('(\$\([^)]*\))', x))]) for x in mylist]
['$(ProjectDir)dir1\\dest1', '$(OutDir)dir2\\dest2', '$(IntDir)dir2\\dest2']

The main thing here is:

[ "".join([
     s if i%2 else s.lower()
     for (i,s) in enumerate(re.split('(\$\([^)]*\))', x))])
   for x in mylist ]

You go through the list mylist and for every x produce it modified version:

[ ... for x in mylist ]

You convert every x using this operation:

"".join([
     s if i%2 else s.lower()
     for (i,s) in enumerate(re.split('(\$\([^)]*\))', x))]

That means: split the string to parts that must be converted (even) and must not be converted (odd).

For example:

>>> re.split('(\$\([^)]*\))', x)
['', '$(ProjectDir)', 'Dir1\\Dest1']

and than enumerate them and convert all even parts:

>>> print list(enumerate(re.split('(\$\([^)]*\))', x)))
[(0, ''), (1, '$(ProjectDir)'), (2, 'Dir1\\Dest1')]

If a part is even or odd you check using this if :

 s if i%2 else s.lower()

Answer 2

If you are allergic to regular expressions...

exclusions = ['$(ProjectDir)', '$(OutDir)', '$(IntDir)']
mylist = ["$(ProjectDir)Dir1\Dest1", "$(OutDir)Dir2\Dest2", "$(IntDir)Dir2\Dest2"]

## Lower case everything
mylist = [s.lower() for s in mylist]

## Revert the exclusions
for patt in exclusions:
    mylist = [s.replace(patt.lower(), patt) for s in mylist]

print mylist