Strings

2. Basic Types: Strings

Strings

In addition to numbers, Python also supports textual data. The typing that includes all forms of text is the #\color{#4271ae}{\mathtt{\text{str}}}# typing, which is short for string.

String definitionIn computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. In most programming languages, a string is contained by quotes.

A string can be of any length; a string can be just a word, a sentence, or an entire body of text.

Creating a stringThe most common way to declare a #\color{#4271ae}{\mathtt{\text{str}}}# is by using either single or double quotes. Internally, there's no difference; it results in exactly the same string:

>>> "Hello, world!"

'Hello, world!'

>>> 'Hello, world!'

'Hello, world!'

When containing a string in one type of quotes, we can use the other type of quotes within the string:

>>> '"Hello, world!" they said.'

'"Hello, world!" they said.'

Note that, when swapping quotes in such a string, this won't result in the same string:

>>> "'Hello, world!' they said."

"'Hello, world!' they said."

Docstrings

A less common way to declare a #\color{#4271ae}{\mathtt{\text{str}}}# is by using a docstring, a type of string that is contained by triple quotes and preserves formatting without the use of special characters. If there's no specific formatting, it will still result in the same string internally:

>>> """Hello, world!"""

'Hello, world!'

If there is formatting, the result will be the same string, but formatted with special characters instead of whitespace. Note that we can use triple single quotes as well.

>>> '''"Hello, world!"
they said.'''

'"Hello, world!"\nthey said.'

Using operators

We can also create strings from several substrings using the #\color{#3e999f} {\mathtt{\text{+}}}# operator. The process of appending strings to strings is also called string concatenation.

>>> "Hello, " + "world!"

'Hello, world!'

Or, if we want a string with a lot of reptition, we can use string multiplication using #\color{#3e999f}{\mathtt{\text{*}}}#.

>>> "0" * 10

'0000000000'

However, when a # \color{#4271ae} {\mathtt{\text{str}}}# is multiplied with any negative number it results in an empty string.

>>> "Hello, world!" * -1

Casting

Strings can also be created through casting. In other words, by converting objects of other types to the #\color{#4271ae}{\mathtt{\text{str}}}# type.

Function Definition
\[\color{#4271ae} {\mathtt{str}}(\textit{object})\]

Where the #\textit{object}# can be of any Python type that supports casting to #\color{#4271ae} {\mathtt{\text{str}}}#.

With this, it is important to realise that the string #\color{#718c00}{\mathtt{\text{"2"}}}# is not the same as the integer #\color{#F5871F}{\mathtt{\text{2}}}#. However, #\color{#F5871F}{\mathtt{\text{2}}}# can be casted to #\color{#718c00}{\mathtt{\text{"2"}}}#, and vice-versa.

>>> str(2) == "2"

True

>>> int("2") == 2

True