Concatenation

Adding strings

+ glues two strings together. It adds nothing of its own, so spaces are up to you:

first = "Ada"
last = "Lovelace"
print(first + last)
print(first + " " + last)

AdaLovelace
Ada Lovelace

Multiplying strings

* repeats:

print("ab" * 3)
print("-" * 20)

ababab
--------------------

A row of dashes as a separator is the everyday use.

Numbers need converting

+ between a string and a number is an error, not an automatic conversion:

age = 36
print("Age: " + str(age))

Age: 36

Without str() that line raises TypeError: can only concatenate str (not "int") to str. Python refuses to guess whether you meant text or arithmetic.

print takes several arguments

Often you do not need to concatenate at all. print accepts a list of things and puts a space between them:

first = "Ada"
age = 36
print(first, age, "years")

Ada 36 years

You can change the separator and the ending:

print("a", "b", "c", sep="-")
print("no newline", end=" -> ")
print("same line")

a-b-c
no newline -> same line

Adjacent literals join themselves

Two string literals next to each other are joined at compile time. This is only for literals, not variables, and it is how long text gets wrapped in source:

message = ("This is one long sentence that would not fit "
           "comfortably on a single line of source code.")
print(message)

This is one long sentence that would not fit comfortably on a single line of source code.

names = ["Ada", "Grace" "Katherine"]
print(len(names))
print(names)

2
['Ada', 'GraceKatherine']

Prefer f-strings

For anything with a variable in it, the next chapter's f-strings are shorter and much easier to read than a chain of +:

first = "Ada"
age = 36
print("Name: " + first + ", age " + str(age))
print(f"Name: {first}, age {age}")

Name: Ada, age 36
Name: Ada, age 36