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.

Answer 1

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)

Answer 2

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)