Repeat a string to a certain length in Python

Repeat a string to a certain length in Python #

To repeat a string to a certain length:

1. Multiply the string by the specified length to repeat it N times.
2. Use string slicing to select a part of the string from index 0 up to the specified length.

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# 👇️ slightly faster for longer strings
# also more difficult to read
def repeat_to_length(string, length):
    return (string * (length//len(string) + 1))[:length]


print(repeat_to_length('asd', 6))  # 👉️ asdasd

print(repeat_to_length('asd', 4))  # 👉️ asda

# ----------------------

# 👇️ slightly slower for longer strings
# much easier to read

def repeat_to_length_2(string, length):
    return (string * length)[:length]


print(repeat_to_length_2('asd', 6))  # 👉️ asdasd

print(repeat_to_length_2('asd', 4))  # 👉️ asda

The first thing to note is that we can repeat a string by multiplying it with an integer.

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print('asd' * 2) # 👉️ 'asdasd'

The first function aims to repeat the string fewer times and might be a little faster for longer strings.

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def repeat_to_length(string, length):
    return (string * (length//len(string) + 1))[:length]


print(repeat_to_length('asd', 6))  # 👉️ asdasd

print(repeat_to_length('asd', 4))  # 👉️ asda

The function takes the string and the desired length as arguments and repeats the string to the specified length.

We used the floor division // operator to get an integer from the division.

Division / of integers yields a float, while floor division // of integers result in an integer.

This is important because division / of integers always returns a float, and trying to multiply a string by a float would raise a TypeError.

The last step is to use string slicing to get a part of the string from index 0 up to the specified length.

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print('asdasd'[:4]) # 👉️ 'asda'
print('asdasd'[:3]) # 👉️ 'asd'

The syntax for string slicing is my_str[start:stop:step], where the start value is inclusive and the stop value is exclusive.

This is exactly what we need, because indexes are zero-based in Python. In other words, the last index in a string is len(my_str) - 1.

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def repeat_to_length_2(string, length):
    return (string * length)[:length]


print(repeat_to_length_2('asd', 6))  # 👉️ asdasd

print(repeat_to_length_2('asd', 4))  # 👉️ asda

We multiply the string by the specified length to repeat it N times.

The string is repeated many more times than necessary, but this is probably not going to be an issue if working with relatively short strings.

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# 👇️ asdasdasdasdasdasd
print('asd' * 6)

# 👇️ asdasd
print('asdasdasdasdasdasd'[:6])

This approach might be slower for longer strings, but it is much easier to read.