CODEWITHSUNDEEP
pythonstring
Gabriel
Gabriel

Reputation: 311

How do I cycle through a list of characters and replace them with "_" in Python?

I am trying to get my Python program to cycle through a list of unwanted characters that I wrote in a list. I want it to use a for functions to replace those characters with "_" in a string.

global string
global OddChars
string = "Parenthesis: () Brackets: []"
OddChars = ["[", "]", "(", ")", " "]

for Replace in OddChars:
       string = string.replace(Replace, "_")
print (string)

I want the new string to have _ instead of ()[] and spaces. When I try this it doesn't work, it prints the same string as before.

Upvotes: 2

Views: 344

Answers (4)

Tanveer Alam
Tanveer Alam

Reputation: 5275

>>> input_string = "Parenthesis: () Brackets: []"
>>> temp_string = ''
>>> odd_chars = ["[", "]", "(", ")", " "]
>>> for odd_char in odd_chars:
...     temp_string = input_string.replace(odd_char, "_")
...     input_string = temp_string
... 
>>> print input_string
Parenthesis:____Brackets:___

I tried to correct your solution. Your logic was little incorrect. After first replace you were not passing updated string for other odd chars in the iteration.

Upvotes: 1

Aaron Hall
Aaron Hall

Reputation: 395075

For this type of operation, use the str.translate method.

Python 2

In Python 2, we use the string module's maketrans function to create a translation table. (Be sure not to overwrite the string module, I changed your variable name, string to mystring below.)

>>> import string
>>> my_string = "Parenthesis: () Brackets: []"
>>> OddChars = ["[", "]", "(", ")", " "] # unused, but I could join for below
>>> string.maketrans('[]() ', '_____') # <- 1st arg would be ''.join(OddChars)
'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f_!"#$%&\'__*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ_\\_^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>> translation_table = string.maketrans('[]() ', '_____')
>>> my_string.translate(translation_table)
'Parenthesis:____Brackets:___'

You could make this into a reusable function:

import string

def replace_chars(my_string, old_chars, new_chars):
    translation_table = string.maketrans(old_chars, new_chars)
    return my_string.translate(translation_table)

Python 3

In Python 3, the string module doesn't have this functionality, it has been moved as a static method to the builtin str (which means you could call it from str or an instance of a string, like my_string below):

>>> my_string = "Parenthesis: () Brackets: []"
>>> translation_table = str.maketrans('[]() ', '_____') # str could be my_string 
>>> translation_table
{40: 95, 41: 95, 91: 95, 93: 95, 32: 95}
>>> my_string.translate(translation_table)
'Parenthesis:____Brackets:___'

The function could look like this:

def replace_chars(my_string, old_chars, new_chars):
    return my_string.translate(str.maketrans(old_chars, new_chars))

Upvotes: 2

c24b
c24b

Reputation: 5552

  1. Simply import regex module in your program
  2. Be careful of using escape caracter \ before the character in you list and transform it to a string to make a string replacement if you don't want to rewrite your list just add "|\".join(OddChar) and the OR option in regex but in your example it's not necessary
  3. Just use the submodule re.sub, Tip:if you want a better performance you can compile your expression by using re.compile

import re

OddChar2str = OddChar.join("|\")

your oddchar is now equivalent to "\(|\)|\[|\]"

replace = re.sub(OddChar2str, '_', string)

Upvotes: 1

uselpa
uselpa

Reputation: 18917

>>> s = "Parenthesis: () Brackets: []"
>>> o = ["[", "]", "(", ")", " "]
>>> "".join(["_" if c in o else c for c in s])
'Parenthesis:____Brackets:___'

Upvotes: 1

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