Python String join()

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Concatenates the elements in an iterable.

Minimal Example

>>> '-'.join(['the', 'answer', 'is', '42'])
'the-answer-is-42'

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

Syntax and Explanation

str.join(iterable)

Concatenates the elements in an iterable. The result is a string whereas each elements in the iterable are “glued together” using the string on which it is called as a delimiter.

To join all elements in an iterable without a delimiter, call ''.join() on the empty string:

>>> ''.join(['1', '2', '3'])
'123'

Here’s the same example with some non-empty delimiters:

>>> ''.join(['1', '2', '3'])
'123'
>>> '-'.join(['1', '2', '3'])
'1-2-3'
>>> '--'.join(['1', '2', '3'])
'1--2--3'
>>> ' + 1 + '.join(['1', '2', '3'])
'1 + 1 + 2 + 1 + 3'

If there are non-string values in the iterable, Python raises a TypeError:

>>> ''.join([1, 2, 3])
Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
    ''.join([1, 2, 3])
TypeError: sequence item 0: expected str instance, int found

To fix the TypeError due to non-string elements in the iterable, convert each element to a string first using list comprehension ''.join([str(x) for x in iterable]) and the built-in str() function before joining the elements.

Here’s an example:

>>> numbers = [1, 2, 3]
>>> ''.join([str(x) for x in numbers])
'123'

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.

MethodDescription
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