Python string join() usage and examples

Python string methods

join() is a string method that returns a string connected with the iterable elements.

The join() method provides a flexible way to concatenate strings. It concatenates each element of the iterable (such as a list, string, and tuple) to the string and returns the concatenated string.

The syntax of join() is:

string.join(iterable)

The join() parameter

The join() method takes an iterable object-Objects that can return their members at once

Some examples of iterable are:

• Native data types - List,Tuple,String,DictionaryAndSet

• File object and usage__iter__ ()or an object defined by the __getitem()__ method

The join() return value

The join() method returns a string concatenated with the elements of the iterable.

If Iterable contains any non-string values, it will triggerTypeErrorException.

Example1：How does the join() method work?

numList = ['1', ''2', ''3', ''4]
seperator = ', ''
print(seperator.join(numList))
numTuple = ('1', ''2', ''3', ''4)
print(seperator.join(numTuple))
s1　= 'abc'
s2　= '123'
""" s2each character is connected to s1in front """　
print('s1.join(s2): ', s1.join(s2))
""" s1each character is connected to s2in front """　
print('s2.join(s1): ', s2.join(s1))

When running the program, the output is:

1,　2,　3,　4
1,　2,　3,　4
s1.join(s2):　1abc2abc3
s2.join(s1): a123b123c

Example2：How does the join() method work in sets?

test =  {2', ''1', ''3}
s = ', ''
print(s.join(test))
test = {'Python', 'Java', 'Ruby'}
s = '->-'
print(s.join(test))

When running the program, the output is:

2,　3,　1
Python->->Ruby->->Java

Note: 　Sets are an unordered collection of items, and you may get different outputs.

Example3：How does the join() method work in dictionaries?

test =  {'mat':　1, 'that':　2}
s = '-'
print(s.join(test))
test =  {1: 'mat',　2: 'that'}
s = ', ''
# This throws an error
print(s.join(test))

When running the program, the output is:

mat->that
Traceback (most recent call last):
　　File "...", line　9, in <module>
TypeError: sequence item 0: expected str instance, int found

The join() method attempts to concatenate the keys of the dictionary (not the values) to the string. If the string key is not a string, it will triggerTypeErrorException.　

Python string methods