str.replace() Function in Python

The str.replace() function in Python is used to replace occurrences of a specified substring with another substring within a string. This function is useful for modifying strings by changing certain parts of them to new values.

Syntax:

string.replace(old, new, count)

• old: The substring you want to replace.
• new: The substring you want to use as the replacement.
• count (optional): An integer specifying the maximum number of occurrences to replace. If omitted, all occurrences of the old substring will be replaced.

Example 1: Basic usage

# Example 1: Replacing a substring
my_string = "Hello, world! Hello, everyone!"
new_string = my_string.replace("Hello", "Hi")
print(new_string)  # Output: "Hi, world! Hi, everyone!"

In this example:

• The substring "Hello" is replaced with "Hi" in the original string.
• Both occurrences of "Hello" are replaced because count is not specified.

Example 2: Specifying the count

# Example 2: Specifying the maximum number of replacements
my_string = "apple banana apple orange apple"
new_string = my_string.replace("apple", "kiwi", 2)
print(new_string)  # Output: "kiwi banana kiwi orange apple"

Here:

• Only the first two occurrences of "apple" are replaced with "kiwi".
• The third occurrence remains unchanged.

Example 3: Replacing with an empty string

# Example 3: Removing a substring
my_string = "Hello, world!"
new_string = my_string.replace("world", "")
print(new_string)  # Output: "Hello, !"

In this case:

• The substring "world" is replaced with an empty string, effectively removing it from the original string.

Key Points:

• str.replace() creates and returns a new string with the specified substitutions; it does not modify the original string.
• The function is case-sensitive, meaning "Hello" and "hello" would be treated as different substrings.
• If the old substring is not found, the original string remains unchanged.
• If the new substring is the same as old, the string remains the same, unless count is specified and there are occurrences of old.

Example 4: Case sensitivity

# Example 4: Case sensitivity
my_string = "Hello, world! hello, everyone!"
new_string = my_string.replace("hello", "hi")
print(new_string)  # Output: "Hello, world! hi, everyone!"

In this example:

• Only the second occurrence of "hello" (with a lowercase "h") is replaced with "hi", while "Hello" (with an uppercase "H") remains unchanged.

Example 5: Replacing non-existent substring

# Example 5: Non-existent substring
my_string = "Hello, world!"
new_string = my_string.replace("foo", "bar")
print(new_string)  # Output: "Hello, world!"

Here:

• Since "foo" is not found in the original string, the output remains the same.