How to Remove Everything After the Last Character in a String?

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Problem Formulation

  • Given string s, and
  • character c.

How to remove all characters in s after the first occurrence of c?

Example

Given:
- string s = 'hello world', and 
- empty space character c = ' '. 

Desired result:
'hello'

Method 1: string.index() + slicing

To remove everything after the first occurrence of character c, determine the index of c in s with s.index(c). Then pass the result as stop index into a slicing operation, starting from the first character such as in s[:s.index(c)]. The result is the substring up to the first occurrence of character c in s, excluded.

# Method 1: string.index() + slicing
s = 'hello world'
c = ' '

result = s[:s.index(c)]

print(result)
# hello

Method 2: string.split()

The method str.split(sep, maxsplit) with maxsplit set to 1 splits the string into two substrings into a list. It splits the string at the first occurrence of the separator argument sep. By accessing the first element of this list, you obtain the string with everything before the first occurrence of the sep character.

# Method 2: string.split()
s = 'hello world'
c = ' '

result = s.split(c, 1)[0]

print(result)
# hello

The string.split(delimiter, maxsplit=1) method creates a list of strings, split at the delimiter string. If you split at delimiter character c, the first element of the split list is the string before the first occurrence of character c. That’s why the operation s.split(c, 1)[0] gives you the string with everything removed after the first occurrence of the character c.

Method 3: Regex

The re.findall(pattern, string) method of Python’s regular expression library re creates a list of strings that match the pattern in the given string. By using the pattern '.*' + c, you match everything up to the first occurrence of the character c. You take the first element of the returned list with the indexing operation ...[0] and determine all characters but the last one (that is the matching character c) by using slicing ...[:-1] up to the second last element.

# Method 3: regex
import re
s = 'hello world'
c = ' '

result = re.findall('.*' + c, s)[0][:-1]

print(result)
# hello

Where to Go From Here?

Enough theory. Let’s get some practice!

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