Using translate(): translate() is another method that can be used to remove a character from a string in Python. translate() returns a string after removing the values passed in the table. Also, remember that to remove a character from a string using translate() you have to replace it with None and not "" .
Use the isalnum() Method to Remove All Non-Alphanumeric Characters in Python String. We can use the isalnum() method to check whether a given character or string is alphanumeric or not. We can compare each character individually from a string, and if it is alphanumeric, then we combine it using the join() function.
Use re.sub
, like so:
>>> import re
>>> re.sub('\D', '', 'aas30dsa20')
'3020'
\D
matches any non-digit character so, the code above, is essentially replacing every non-digit character for the empty string.
Or you can use filter
, like so (in Python 2):
>>> filter(str.isdigit, 'aas30dsa20')
'3020'
Since in Python 3, filter
returns an iterator instead of a list
, you can use the following instead:
>>> ''.join(filter(str.isdigit, 'aas30dsa20'))
'3020'
In Python 2.*, by far the fastest approach is the .translate
method:
>>> x='aaa12333bb445bb54b5b52'
>>> import string
>>> all=string.maketrans('','')
>>> nodigs=all.translate(all, string.digits)
>>> x.translate(all, nodigs)
'1233344554552'
>>>
string.maketrans
makes a translation table (a string of length 256) which in this case is the same as ''.join(chr(x) for x in range(256))
(just faster to make;-). .translate
applies the translation table (which here is irrelevant since all
essentially means identity) AND deletes characters present in the second argument -- the key part.
.translate
works very differently on Unicode strings (and strings in Python 3 -- I do wish questions specified which major-release of Python is of interest!) -- not quite this simple, not quite this fast, though still quite usable.
Back to 2.*, the performance difference is impressive...:
$ python -mtimeit -s'import string; all=string.maketrans("", ""); nodig=all.translate(all, string.digits); x="aaa12333bb445bb54b5b52"' 'x.translate(all, nodig)'
1000000 loops, best of 3: 1.04 usec per loop
$ python -mtimeit -s'import re; x="aaa12333bb445bb54b5b52"' 're.sub(r"\D", "", x)'
100000 loops, best of 3: 7.9 usec per loop
Speeding things up by 7-8 times is hardly peanuts, so the translate
method is well worth knowing and using. The other popular non-RE approach...:
$ python -mtimeit -s'x="aaa12333bb445bb54b5b52"' '"".join(i for i in x if i.isdigit())'
100000 loops, best of 3: 11.5 usec per loop
is 50% slower than RE, so the .translate
approach beats it by over an order of magnitude.
In Python 3, or for Unicode, you need to pass .translate
a mapping (with ordinals, not characters directly, as keys) that returns None
for what you want to delete. Here's a convenient way to express this for deletion of "everything but" a few characters:
import string
class Del:
def __init__(self, keep=string.digits):
self.comp = dict((ord(c),c) for c in keep)
def __getitem__(self, k):
return self.comp.get(k)
DD = Del()
x='aaa12333bb445bb54b5b52'
x.translate(DD)
also emits '1233344554552'
. However, putting this in xx.py we have...:
$ python3.1 -mtimeit -s'import re; x="aaa12333bb445bb54b5b52"' 're.sub(r"\D", "", x)'
100000 loops, best of 3: 8.43 usec per loop
$ python3.1 -mtimeit -s'import xx; x="aaa12333bb445bb54b5b52"' 'x.translate(xx.DD)'
10000 loops, best of 3: 24.3 usec per loop
...which shows the performance advantage disappears, for this kind of "deletion" tasks, and becomes a performance decrease.
s=''.join(i for i in s if i.isdigit())
Another generator variant.
You can use filter:
filter(lambda x: x.isdigit(), "dasdasd2313dsa")
On python3.0 you have to join this (kinda ugly :( )
''.join(filter(lambda x: x.isdigit(), "dasdasd2313dsa"))
along the lines of bayer's answer:
''.join(i for i in s if i.isdigit())
You can easily do it using Regex
>>> import re
>>> re.sub("\D","","£70,000")
70000
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