Python String Concatenation

In Python, we can concatenate strings using the + operator. The + operator allows us to add two or more strings together. Let’s look at some examples.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = string1 + string2
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
HelloWorld

In the above example, we have concatenated two strings using the + operator. The + operator concatenates the second string to the end of the first string.

Adding a Space

We can add a space between two strings by adding an empty string ("" or '') to the first string. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = string1 + " " + string2
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
Hello World

In the above example, we have concatenated two strings with a space in between. We have added an empty string ("") with a space in between to the first string.

Concatenate Strings of Different Data Types

We can concatenate strings of different data types in Python. But we need to convert the non-string data types to strings before concatenating them. We can use the str() function to convert non-string data types to strings. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
number = 5
# concatenate strings
string2 = string1 + str(number)
print(string2)

Output:

command

C:\Users\Your Name> python strings.py
Hello5

In the above example, we have concatenated a string and an integer. We have converted the integer to a string using the str() function before concatenating it with the string.

Concatenate Strings Using join()

We can also concatenate strings using the join() method. The join() method takes an iterable as an argument and concatenates the elements of the iterable to the string. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = "".join([string1, string2])
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
HelloWorld

In the above example, we have concatenated two strings using the join() method. We have passed a list of strings to the join() method. The join() method has concatenated the strings in the list and returned the concatenated string.

sketch Building a string: join wins, and one stray reference wrecks everything p5.js Pause Restart

Three ways to build the same 100,000-character string. join is the fastest because it allocates once. Plain += is not the disaster folklore claims -- CPython can often resize the string in place -- but that optimisation needs the string to have exactly one reference, and keeping a second one anywhere in the loop switches it off. Then every += copies the whole string and the cost becomes quadratic. Measured: 8.90 ms, 3.52 ms, and 114.38 ms.

Concatenate Strings Using f-strings

We can also concatenate strings using f-strings. f-strings are string literals that have an f at the beginning and curly braces ({}) containing expressions that will be replaced with their values. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = f"{string1} {string2}"
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
Hello World

In the above example, we have concatenated two strings using f-strings. We have used curly braces ({}) to insert the values of the variables into the string.

Note

f-strings are faster than other string concatenation methods. So, it is recommended to use f-strings for string concatenation. f-string is the most preferred way of string concatenation in Python. We can use f-strings to concatenate strings of different data types as well. Let’s look at an example. f-string uses f{expression} to insert the value of an expression into a string. We use f-string to print and insert variables into a string. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
number = 5
# concatenate strings
string2 = f"{string1} {number}" # variables are also expressions
print(string2)

Output:

command

C:\Users\Your Name> python strings.py
Hello 5

In the above example, we have concatenated a string and an integer using f-strings. We have inserted the value of the variable string1 and number into the string using f-strings.

Tip

f-strings are available in Python 3.6 and above. If you are using an older version of Python, you can use the format() method to concatenate strings. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = "{} {}".format(string1, string2)
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
Hello World

In the above example, we have concatenated two strings using the format() method. We have used curly braces ({}) to insert the values of the variables into the string.

Concatenate Strings Using % Operator

We can also concatenate strings using the % operator. The % operator is also known as the string formatting operator. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = "%s %s" % (string1, string2)
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
Hello World

In the above example, we have concatenated two strings using the % operator. We have used %s to insert the values of the variables into the string.

Tip

The % operator is available in Python 2 and Python 3. But it is recommended to use f-strings for string concatenation in Python 3.6 and above.

Concatenate Strings Using String Slicing

We can also concatenate strings using string slicing. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = string1[:2] + string2[2:]
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
HeloWorld

String Concatenation in a Loop

We can also concatenate strings in a loop. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = ""
for i in range(5):
    string3 += string1 + string2
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
HelloWorldHelloWorldHelloWorldHelloWorldHelloWorld

In the above example, we have concatenated two strings in a loop. We have used the += operator to concatenate the strings in the loop.

Is += in a loop slow? Not usually — but it can fall off a cliff

The common advice is that += in a loop is quadratic. On CPython that is not what happens: the interpreter can resize the string in place, so building 100,000 characters measured 8.90 ms — slower than "".join(...) at 3.52 ms, but nowhere near quadratic.

The in-place trick only works while the string has exactly one reference. Keep a second one anywhere in the loop and it switches off:

alias.py

s = ""
keep = None
for i in range(100_000):
    keep = s          # <- a second reference; now every += copies the whole string
    s += "x"

That measured 114.38 ms — about 13x slower than the same loop without the alias. The alias can be innocent: a debug list, a “previous value” variable, a closure capture.

join avoids the question entirely, and is the only version whose cost does not depend on a CPython implementation detail.

Multiline String Concatenation

We can also concatenate multiline strings in Python. Let’s look at an example.

strings.py

# define strings
string1 = """Hello
World"""
string2 = """Hello
World"""
# concatenate strings
string3 = string1 + string2
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
Hello
WorldHello
World

Multiple String Concatenation

We can also concatenate multiple strings in Python. Let’s look at an example.

strings.py

# define strings
string1 = "Hello"
string2 = "World"
# concatenate strings
string3 = string1 * 3 + string2 * 2
print(string3)

Output:

command

C:\Users\Your Name> python strings.py
HelloHelloHelloWorldWorld

In the above example, we have concatenated multiple strings. We have used the * operator to concatenate the strings.

Conclusion

In this tutorial, we have learned how to concatenate strings in Python. We have also learned how to concatenate strings of different data types in Python. Now you can solve problems that require string concatenation in Python. 🎉

Try it: String Concatenation Exercises

Exercise 1 – Concatenate with +

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Exercise 2 – Join a List of Strings

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Exercise 3 – Repeat a String

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