NumPy strings.isalnum()

The numpy.strings.isalnum() function checks whether all characters in each element of an input array are alphanumeric (letters and numbers) and whether there is at least one character. If all characters in a string are alphanumeric, it returns True; otherwise, it returns False.

Syntax

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numpy.strings.isalnum(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True)

Parameters

Parameter	Type	Description
`x`	array_like (StringDType, bytes_ or str_ dtype)	Input array containing strings to check.
`out`	ndarray, None, or tuple of ndarray and None, optional	Optional output array where the result is stored. If None, a new array is created.
`where`	array_like, optional	Boolean mask specifying which elements to evaluate. Elements where `where=False` retain their original value.
`casting`	str, optional	Defines the casting behavior during computation.
`order`	str, optional	Specifies memory layout order of the output array.
`dtype`	data-type, optional	Defines the data type of the output array.
`subok`	bool, optional	Determines whether subclasses of ndarray are preserved in the output.

Return Value

Returns an array of boolean values where True indicates that all characters in the corresponding input string are alphanumeric, and False otherwise. If the input is a scalar, the output is a scalar boolean.

Examples

1. Checking Alphanumeric Strings in an Array

In this example, we check if each string in an array contains only alphanumeric characters.

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import numpy as np

# Define an array of strings
fruits = np.array(["apple", "banana123", "cherry!", "mango"])

# Check if each string is alphanumeric
result = np.char.isalnum(fruits)

# Print the results
print("Input strings:", fruits)
print("Alphanumeric check:", result)

Output:

Input strings: ['apple' 'banana123' 'cherry!' 'mango']
Alphanumeric check: [ True  True False  True]

The string "cherry!" contains a non-alphanumeric character (!), so the result for that element is False. All other strings contain only letters and numbers, so their results are True.

2. Using the `out` Parameter

Using an output array to store results instead of creating a new array.

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import numpy as np

# Define an array of strings
words = np.array(["grape", "pineapple", "kiwi!", "berry123"])

# Create an output array with the same shape
output_array = np.empty_like(words, dtype=bool)

# Compute isalnum and store the result in output_array
np.char.isalnum(words, out=output_array)

# Print the results
print("Computed isalnum values:", output_array)

Output:

Computed isalnum values: [ True  True False  True]

Here, "kiwi!" contains a non-alphanumeric character (!), so its result is False.

3. Using the `where` Parameter

Using a condition to evaluate only selected elements.

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import numpy as np

# Define an array of strings
items = np.array(["apple1", "banana!", "cherry", "grape$"])

# Define a mask (evaluate only where mask is True)
mask = np.array([True, False, True, False])

# Compute isalnum only where mask is True
result = np.char.isalnum(items, where=mask)

# Print the results
print("Computed isalnum values with mask:", result)

Output:

Computed isalnum values with mask: [ True False  True False]

The function evaluates only the elements where the mask is True, ignoring others.

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NumPy strings.isalnum() – AlphaNumeric Check in String Array