Python String isalnum() – Be on the Right Side of Change

Checks whether all characters are alphabetic or numeric (True or False).

Minimal Example

>>> '000111finxter'.isalnum()
True

As you read over the explanations below, feel free to watch our video guide about this particular string method:

Syntax and Explanation

str.isalnum()

Checks whether all characters are alphabetic or numeric (True or False). More specifically, a character c is alphanumeric if one of the following string methods returns True:

c.isalpha() – Checks whether all characters are alphabetic (True or False).
c.isdecimal() – Checks whether all characters are decimal numbers (True or False).
c.isdigit() – Checks whether all characters are digits, i.e., numbers from 0 to 9 (True or False).
c.isnumeric() – Checks whether all characters are numeric values (True or False).

In other words, a semantically identical implementation of isalnum(c) would be:

def isalnum(c):
    return c.isalpha() or c.isdecimal() or c.isdigit() or c.isnumeric()

More String Methods

Python’s string class comes with a number of useful additional string methods. Here’s a short collection of all Python string methods—each link opens a short tutorial in a new tab.

Method	Description
`capitalize()`	Return a copy of the string with capitalized first character and lowercased remaining characters.
`casefold()`	Return a lowercased, casefolded string similar to `lowercase()` but more aggressive.
`center()`	Return a centered string of a certain length, padded with whitespace or custom characters.
`count()`	Return the number of non-overlapping occurrences of a substring.
`encode()`	Returns a byte object that is an encoded version of the string.
`endswith()`	Returns whether the string ends with a given value or not (`True` or `False`).
`expandtabs()`	Return a string with spaces instead of tab characters.
`find()`	Returns the index of the first occurrence of the specified substring.
`format()`	Formats the string according to the Format Description Language.
`format_map()`	Formats the string according to the Format Description Language, passing a mapping object.
`index()`	Returns the index of the first occurrence of the specified substring, like `find()` but it raises a `ValueError` if the substring is not found.
`isalnum()`	Checks whether all characters are alphabetic or numeric (`True` or `False`).
`isalpha()`	Checks whether all characters are alphabetic (`True` or `False`).
`isascii()`	Checks whether all characters are ASCII (`True` or `False`).
`isdecimal()`	Checks whether all characters are decimal numbers (`True` or `False`).
`isdigit()`	Checks whether all characters are digits, i.e., numbers from 0 to 9 (`True` or `False`).
`isidentifier()`	Checks whether all characters are identifiers that can be used as names of functions, classes, or variables (`True` or `False`).
`islower()`	Checks whether all characters are lowercase (`True` or `False`).
`isnumeric()`	Checks whether all characters are numeric values (`True` or `False`).
`isprintable()`	Checks whether all characters are printable (`True` or `False`).
`isspace()`	Checks whether all characters are whitespaces (`True` or `False`).
`istitle()`	Checks if the string is title-cased (`True` or `False`).
`isupper()`	Checks whether all characters are uppercase (`True` or `False`).
`join()`	Concatenates the elements in an iterable.
`ljust()`	Returns a left-justified string filling up the right-hand side with fill characters.
`lower()`	Returns a lowercase string version.
`lstrip()`	Trims whitespaces on the left and returns a new string.
`maketrans()`	Returns a translation table.
`partition()`	Searches for a separator substring and returns a tuple with three strings: (1) everything before the separator, (2) the separator itself, and (3) everything after it.
`removeprefix()`	Return `string[len(prefix):]` if the string starts with `prefix`, and `string[:]` otherwise.
`removesuffix()`	Return `string[:-len(suffix)]` if the string starts with `suffix`, and `string[:]` otherwise.
`replace()`	Returns a string with replaced values.
`rfind()`	Return the highest index in the string where a substring is found. Returns `-1` if not found.
`rindex()`	Return the highest index in the string where a substring is found. Returns `ValueError` if not found.
`rjust()`	Returns a right-justified string filling up the left-hand side with fill characters.
`rpartition()`	Searches for a separator substring and returns a tuple with three strings: (1) everything before the separator, (2) the separator itself, and (3) everything after it.
`rsplit()`	Splits the string at a given separator and returns a split list of substrings.
`rstrip()`	Trims whitespaces on the right and returns a new string.
`split()`	Splits the string at a given separator and returns a split list of substrings.
`splitlines()`	Splits the string at line breaks such as `'\n'` and returns a split list of substrings (i.e., lines).
`startswith()`	Returns whether the string starts with a given value or not (`True` or `False`).
`strip()`	Trims whitespaces on the left and right and returns a new string.
`swapcase()`	Swaps lowercase to uppercase characters and vice versa.
`title()`	Returns a new string with uppercase first characters of each word.
`translate()`	Returns a translated string.
`upper()`	Returns a lowercase string version.
`zfill()`	Fills the string from the left with `"0"` characters.

References

https://docs.python.org/3/library/stdtypes.html