Replacing multiple characters at once

An option that requires no looping or regular expressions is translate:

>>> "foo_faa:fee,fii".translate(str.maketrans('', '', "_:,"))
"foofaafeefii"

Note that for Python 2, the API is slightly different.

Not directly with replace, but you can build a regular expression with a character class for those characters and substitute all of them at once. This is likely to be more efficient than a loop, too.

>>> import re
>>> re.sub(r"[_:,]+", "", "foo_faa:fee,fii")
'foofaafeefii'

You can try with a loop:

replace_list = ["_", ":", ","]
my_str = "foo_faa:fee,fii"
for i in replace_list:
    my_str = my_str.replace(i, "")

If your only goal is to replace the characters by "", you could try:

''.join(c for c in "foo_faa:fee,fii" if c not in ['_',':',','])

Or alternatively using string.translate (with Python 2):

"foo_faa:fee,fii".translate(None,"_:,")

You should use regex for such kind of operations

import re

s = "foo_faa:fee,fii"

print(re.sub("_*|:*|,*", "", s))