NumPy strings.zfill() – Left Fill String with Zeroes to Specific Length

NumPy strings.zfill()

The numpy.strings.zfill() function left-fills a numeric string with zeros up to the specified width. If the string contains a sign (+/-), the padding is inserted after the sign.

Syntax

numpy.strings.zfill(a, width)

Parameters

Parameter	Type	Description
a	array-like (StringDType, bytes_, or str_)	Input array containing string values to be zero-filled.
width	array_like (integer dtype)	Desired total width of the string after zero-padding.

Return Value

Returns an ndarray containing the input strings left-filled with zeros up to the specified width.

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Examples

1. Zero-Filling a Single String

Here, we left-fill the string 'apple' with zeros to make its length 10.

import numpy as np

# Define a single string
fruit = np.array('apple', dtype='str')

# Apply zfill to make the total length 10
result = np.strings.zfill(fruit, 10)

# Print the result
print("Zero-filled string:", result)

Output:

Zero-filled string: 00000apple

2. Zero-Filling an Array of Strings

We apply zfill to multiple fruit names, ensuring each has a length of 8.

import numpy as np

# Define an array of fruit names
fruits = np.array(['apple', 'banana', 'cherry'], dtype='str')

# Apply zfill to make all strings of length 8
result = np.strings.zfill(fruits, 8)

# Print the results
print("Zero-filled strings:", result)

Output:

Zero-filled strings: ['000apple' '00banana' '00cherry']

3. Zero-Filling Strings with Numeric Values

We use zfill to pad numeric strings while preserving sign placement.

import numpy as np

# Define an array with numeric strings (including a signed number)
numbers = np.array(['42', '-5', '+78'], dtype='str')

# Apply zfill to ensure a width of 5 characters
result = np.strings.zfill(numbers, 5)

# Print the results
print("Zero-filled numeric strings:", result)

Output:

Zero-filled numeric strings: ['00042' '-0005' '+0078']

The numeric values are padded with zeros, and the signs are maintained correctly.