Python function isalnum example usage summary

This article will detail the use of the Python function isalnum and its internal implementation principles from several aspects.

I. Functions and their roles

The isalnum() function is a built-in function in Python that determines whether a string consists of only numbers and letters. If it is, it returns True, otherwise it returns False.

()

where str is the string to be judged.

This function is used to detect whether the string contains non-numeric and alphabetic characters, and returns False if they are present.

II. Function Usage

1. Detection of purely alphabetic and purely numeric strings

This function returns True when the string contains only letters or numbers.

str1 = "HelloWorld"
str2 = "123456"
print(()) # True
print(()) # True

In the above code, str1 contains only letters and str2 contains only numbers, both return True.

2. Detection of strings containing letters and numbers

This function returns True when the string contains both letters and numbers.

str3 = "Hello123World"
print(()) # True

The above code, str3 contains both letters and numbers and returns True.

3. Detection of strings containing special characters

This function returns False when there are non-numeric and alphabetic characters in the string.

str4 = "Hello_World"
print(()) # False

In the above code, str4 contains the underscore character, which is not a number or letter, and returns False.

III. Internal realization principle

isalnum () function of the internal implementation of the principle is relatively simple, in fact, is to iterate through the string of each character, if the character is not a number or letter, then return False, otherwise continue to iterate, and ultimately return True.

def isalnum(self) -> bool:
    """Return True if all characters in the string are alphanumeric
    and there is at least one character, False otherwise.
    A character c is alphanumeric if one of the following holds:
        - c is a letter and isalpha() returns True
        - c is a digit and isdigit() returns True
    """
    if not self:
        return False
    for c in self:
        if not ():
            return False
    return True

As shown above, the implementation of the function is to iterate through the string of each character, and then call the character isalnum () method to determine whether it is a number or letter, if not then return False, otherwise continue to iterate, and ultimately return True.

IV. Conclusion

isalnum() function is a built-in function in Python, used to determine whether the string consists of only numbers and letters, its internal implementation principle is relatively simple, just iterate over each character in the string can be. We can use this function to determine whether a string meets the requirements, so as to quickly realize some string processing functions.

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