How do you remove a letter from a number in python?

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.

Sometimes we want to remove all occurrences of a character from a string. There are two common ways to achieve this.

Python Remove Character from String

1. Using string replace() function
2. Using string translate() function

Python Remove Character from String using replace()

We can use string replace() function to replace a character with a new character. If we provide an empty string as the second argument, then the character will get removed from the string. Note that the string is immutable in Python, so this function will return a new string and the original string will remain unchanged.

s = 'abc12321cba'

print(s.replace('a', ''))

Output: bc12321cb

Python Remove Character from String using translate()

Python string translate() function replace each character in the string using the given translation table. We have to specify the Unicode code point for the character and ‘None’ as a replacement to remove it from the result string. We can use ord() function to get the Unicode code point of a character.

s = 'abc12321cba'

print(s.translate({ord('a'): None}))

Output: bc12321cb If you want to replace multiple characters, that can be done easily using an iterator. Let’s see how to remove characters ‘a’, ‘b’ and ‘c’ from a string.

s = 'abc12321cba'

print(s.translate({ord(i): None for i in 'abc'}))

Output: 12321

Removing Spaces from a String

s = ' 1 2 3 4 '
print(s.replace(' ', ''))  # 1234
print(s.translate({ord(i): None for i in ' '}))  # 1234

Python Remove newline from String

s = 'ab\ncd\nef'
print(s.replace('\n', ''))
print(s.translate({ord('\n'): None}))

Remove substring from string

String replace() function arguments is string. Let’s see how to remove a word from a string.

s = 'ab12abc34ba'
print(s.replace('ab', ''))

Output: 12c34ba

Remove specified number of times

We can also pass a third parameter in replace() function to specify the number of times replacement should be performed.

s = 'abababab'
print(s.replace('a', 'A', 2))

Output: AbAbabab

You can checkout complete python script and more Python examples from our GitHub Repository.

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