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How to Get the First N Characters of a String in Python

Extracting a substring from the beginning of a string is a common operation.

This guide explains how to get the first N characters of a string in Python, primarily using string slicing, the most efficient and Pythonic method. We'll also briefly cover a less efficient for loop approach for comparison.

String slicing is the most direct, efficient, and Pythonic way to get the first N characters. The syntax is string[:n].

string = 'tutorialreference.com'

first_2 = string[:2]  # Get the first 2 characters
print(first_2)        # Output: tu

first_3 = string[:3]  # Get the first 3 characters
print(first_3)        # Output: tut

first_5 = string[:8]  # Get the first 8 characters
print(first_5)        # Output: tutorial
  • string[:n] creates a new string consisting of characters from the beginning of string up to (but not including) index n.
  • String slicing is generally very fast in Python, so it's the best for most use cases.

Handling Edge Cases​

  • n is larger than the string length: If n is greater than the string's length, slicing simply returns the entire string. No error occurs.

    string = 'tutorialreference.com'
    print(string[:100])  # Output: tutorialreference.com

  • Empty string: Slicing an empty string always returns an empty string, regardless of n.

    string = ''
    print(repr(string[:100]))  # Output: ''

Getting the Remainder​

To get the remainder of the string after first n characters, use slicing again, this time with a start index:

string = 'tutorialreference.com'

n = 8
first_8 = string[:n]  # first 8 characters
print(first_8)
after = string[n:]    # remainder
print(after)

Output:

tutorial
reference.com
  • The slice string[:8] will return a new string that starts at index 0 and goes up to, but not including, index 8.
  • The slice string[n:] will start at index 8 and go until the end of the string.

Getting the First N Characters with a for Loop (Less Efficient)​

While slicing is preferred, you can use a for loop. This is much less efficient and less readable, so it's generally not recommended unless you have a very specific reason to do so:

string = 'tutorialreference.com'
first_n = ''
n = 8

for char in string:
    if n < 1:
        break  # Stop when we've collected n characters
    n -= 1
    first_n += char

print(first_n)  # Output: tutorial
  • This will loop until the variable n becomes less than 1.
  • This approach is significantly less efficient than slicing, and harder to read. Avoid it unless you have a compelling reason.

Creating a reusable function​

You can also create a function that accepts a string and a number n, and returns the slice containing first n characters:

def get_first_n(string, n):
    return string[:n]

string = 'tutorialreference.com'

print(get_first_n(string, 2)) # Output: tu
print(get_first_n(string, 3)) # Output: tut
print(get_first_n(string, 8)) # Output: tutorial
  • This approach is useful if you have to perform this operation multiple times in your code.

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