Filtering Characters from a String [duplicate]

Question

I need to make a function that takes two strings as imnput and returns a copy of str 1 with all characters from str2 removed.

First thing is to iterate over str1 with a for loop, then compare to str2, to accomplish subtraction I should create a 3rd string in which to store the output but I'm a little lost after that.

def filter_string(str1, str2): str3 = str1 for character in str1: if character in str2: str3 = str1 - str2 return str3

This is what I've been playing with but I don't understand how I should proceed.

Community · Accepted Answer · 2020-06-20 09:12:55Z

Just use str.translate():

In [4]: 'abcdefabcd'.translate(None, 'acd') Out[4]: 'befb'

From the documentation:

string.translate(s, table[, deletechars]) 
Delete all characters from s that are in deletechars (if present), and then translate the characters using table, which must be a 256-character string giving the translation for each character value, indexed by its ordinal. If table is None, then only the character deletion step is performed.

If -- for educational purposes -- you'd like to code it up yourself, you could use something like:

''.join(c for c in str1 if c not in str2)

This works and I understand how but I don't think it was strictly how I was supposed to achieve it.
In Python3 the translate function only takes one argument, see docs.python.org/3/library/… . To do the same thing in Python 3 you need to do: 'abcdefabcd'.translate(str.maketrans({'a': None, 'c': None, 'd': None})) , see also stackoverflow.com/questions/41535571/…
This is for Python2. for python3: text = text.translate(str.maketrans('','',string.punctuation))

Konstantin · Accepted Answer · 2017-12-11 08:35:46Z

Use replace:

def filter_string(str1, str2): for c in str2: str1 = str1.replace(c, '') return str1

Or a simple list comprehension:

''.join(c for c in str1 if c not in str2)

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