Replacing Characters in a String Using Dictionary in Python

In Python, we can replace characters in a string dynamically based on a dictionary. Each key in the dictionary represents the character to be replaced, and its value specifies the replacement. For example, given the string "hello world" and a dictionary {'h': 'H', 'o': 'O'}, the output would be "HellO wOrld". Let's explore several ways to achieve this.

Using str.translate() with str.maketrans()

This method uses Python's built-in str.translate() and str.maketrans() methods to replace characters efficiently.

s = "hello world"
replacements = {'h': 'H', 'o': 'O'}
# Create translation table and replace characters
res = s.translate(str.maketrans(replacements))
print(res)

HellO wOrld

Explanation:

• str.maketrans() method creates a translation table from the dictionary.
• str.translate() method applies the translation table to the string, replacing the specified characters.

Let's explore some more ways and see how we can replace characters in a string using dictionary in Python.

Using List Comprehension with join()

We can iterate through the string and replace characters based on the dictionary using a list comprehension.

s = "hello world"
replacements = {'h': 'H', 'o': 'O'}
# Replace characters and join back to a string
res = ''.join(replacements.get(c, c) for c in s)
print(res)

GFG!

Explanation:

• The get method retrieves the replacement for a character if it exists in the dictionary; otherwise, it keeps the original character.
• join() method combines the updated characters into a single string.

Using For Loop

This approach uses a traditional for loop to iterate through the string and replace characters.

s = "hello world"
replacements = {'h': 'H', 'o': 'O'}
res = ""
# Replace characters manually
for c in s:
    res += replacements.get(c, c)
print(res)

HellO wOrld

Explanation:

• for loop iterates through each character in the string.
• Get method checks if the character has a replacement; otherwise, it appends the original character.

Using Regular Expressions

If the dictionary keys contain multiple characters or patterns, re.sub() can be used for replacements.

import re
s = "hello world"
replacements = {'h': 'H', 'o': 'O'}
# Create a regular expression pattern from the dictionary keys
pattern = re.compile('|'.join(re.escape(k) for k in replacements))
# Replace characters using the pattern
res = pattern.sub(lambda x: replacements[x.group(0)], s)
print(res)

HellO wOrld

Explanation:

• re.escape() method ensures special characters in the dictionary keys are escaped properly.
• sub() method replaces matches with corresponding values from the dictionary.