Learning Python is fun

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So we’ve seen numbers, but what about text?
'string' is the data type we use to store and use text in Python.

A piece of text is called a string, and you can perform all kinds of operations on a string. Let’s start with the basics first!

A string is a sequence of characters.

In simple terms, a string is a piece of text. Strings are not just a Python thing. It’s a well-known term in computer science and means the same thing in most of the other languages.

String declaration

A Python string needs quotes around it for it to be recognized as such, like this:

>>> 'Hello, World'
'Hello, World'

Because of the quotes, Python understands this is a sequence of characters and not a command, number, or variable.

And just like with numbers, some of the operators we learned before work on Python strings, too. Try it with the following expressions:

>>> 'a' + 'b'
'ab'
>>> 'ab' * 4
'abababab'
>>> 'a' - 'b'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'str' and 'str'

Double quotes

We’ve used single quotes, but Python accepts double quotes around a string as well:

>>> "a" + "b"
'ab'

Note that these are not two single quotes next to each other. The character is often found next to the enter key on your keyboard (US keyboard layout) or on the 2 key (UK layout). It might differ for other countries. You must press shift with this key to get a double quote.

As you can see from its answer, the Python REPL prefers single quotes. It looks clearer, and Python tries to be as clear and well-readable as possible. So why does it support both? It’s because it allows you to use strings that contain a quote.

>>> text1 = "It's a dog"
>>> text2 = 'It's a cat'
  File "<stdin>", line 1
    text2 = 'It's a cat'
                ^
SyntaxError: invalid syntax

we used double quotes to create text1 and there was no problem with the single quote in the word it’s.

but when we tried to create text2 with single quotes we run into trouble.
Python sees the quote in the word it’s and thinks that it's the end of the string!
The following letter, s, causes a Syntax Error.

A syntax error is a character or string that is placed incorrectly in a command or instruction, and that causes a failure in execution.

In other words, Python doesn’t understand the s because it expects the string to have ended and so it fails with the error.

>>> 'It's a black cat'
  File "<stdin>", line 1
    'It's a black cat'
        ^
SyntaxError: invalid syntax

Python points out the exact location of where it encountered the error with the ^ symbol. Python errors tend to be very helpful, so look closely at them. You’ll often be able to pinpoint what’s going wrong.

Even the syntax highlighter on this website gets confused because of the invalid syntax!

So one way to deal with this syntax error is to just use double quotes.
But what if we wanted text that contains both single and double quotes?
He said "It's not possible"

>>> text = 'It\'s a green cat, would you believe it?'
>>> text
"It's a green cat, would you believe it?"

>>> text = "He said \"It's not possible\""
>>> text
'He said "It\'s not possible"'

So should you use single or double quotes? which one should you use? It’s simple: always opt for the option where you need the least amount of escapes, because these escapes make your Python strings less readable.

Python also has syntax for creating multiline strings using triple quotes. By this, I mean three double quotes or three single quotes; both work, but I’ll demonstrate with double quotes:

>>> """This text,
... has many lines...
... more than 2."""
'This text,\nhas many lines...\nmore than 2.'

>>> '''This text,
... also has many lines...
... more than 2.'''
'This text,\nhas many lines...\nmore than 2.'

The following table lists a couple of the most common escape sequences you will encounter:

>>> text = '''He's question was: "How can I escape without back slashes?"'''

String operations

Strings come with several handy, built-in operations (also referred to as methods) you can execute. I’ll show you only a couple here since I don’t want to divert your attention too much.

In the REPL, you can sometimes use auto-completion. Whether it works or not depends on which installer you used to install Python and which OS you are on. Your best bet is to try!

create a string s, on the next line type its name and hit the TAB key twice:

>>> s = ""
>>> s.
s.capitalize(    s.find(          s.isdecimal(     s.istitle(       s.partition(     s.rstrip(        s.translate(
s.casefold(      s.format(        s.isdigit(       s.isupper(       s.replace(       s.split(         s.upper(
s.center(        s.format_map(    s.isidentifier(  s.join(          s.rfind(         s.splitlines(    s.zfill(
s.count(         s.index(         s.islower(       s.ljust(         s.rindex(        s.startswith(
s.encode(        s.isalnum(       s.isnumeric(     s.lower(         s.rjust(         s.strip(
s.endswith(      s.isalpha(       s.isprintable(   s.lstrip(        s.rpartition(    s.swapcase(
s.expandtabs(    s.isascii(       s.isspace(       s.maketrans(     s.rsplit(        s.title(

Most IDEs like Pycharm and VS Code also support auto-completion

In case that didn't work, you can run use the dir and print functions to list all the valid operation our string is supporting

>>> s = ''
>>> print(dir(s))
['capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format',
 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower',
 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip',
 'maketrans', 'partition', 'removeprefix', 'removesuffix', 'replace', 'rfind', 'rindex', 'rjust',
 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase',
 'title', 'translate', 'upper', 'zfill']
>>>

for further and more detailed information on string operations (with an explanation) check out the official Python manual.

>>> 'hello'.upper()
'HELLO'

>>> 'WORLD'.lower()
'HELLO'

>>> len('Hello there')
11
>>> s = 'Jonny English'
>>> len(s)
13

>>> 'I like apple pies'.split(' ')
['I', 'like', 'apple', 'pies']

>>> 'Hello \t\n there,\t\n\n General Kenobi'.split()
['Hello', 'there,', 'General', 'Kenobi']

>>> 'I, am a Jedi!'.replace('Jedi', 'Cookie')
'I, am a Cookie!'
>>> 'Hello =)'.replace('l', '1')
'He11o =)'
>>> 'Get to the chopper!'.replace('chopper', 'choppah')
'Get to the choppah!'

>>> s = 'Python'
>>> s[0]
'P'
>>> s[1]
'y'
>>> s[2]
't'
>>> s[3]
'h'
>>> s[4]
'o'
 >>> s[5]
'n'

>>> s = 'Python'
>>> s[0:2]
'Py'
>>> s[2:4]
'th'
>>> s[4:]
'thon'

the step_size defaults to 1. we can test that by running the same slices as before but with a step_size of 1

>>> s = 'Python'
>>> s[0:2:1]
'Py'
>>> s[2:4:1]
'th'
>>> s[4::1]
'thon'

>>> s = 'Python'
>>> s[0:2:1]
'Py'
>>> s[0:2]
'Py'
>>> s[0:2:]
'Py'

Let's see more realistic usages with the step_size

>>> s[::2]
'Pto'
>>> s[1::2]
'yhn'

>>> s = 'Python'
>>> s[::-1]
'nohtyP'

>>> 'Hi, Jack'.replace('Jack', 'Lola').upper()
'HI LOLA'

>>> price = 40
>>> product = 'Shoes'
>>> f'{product} cost {price}$'
'Shoes cost 40$'

Proving your skills

Just like before, I have gathered some basic challenges for you to go over.

We learned how to deal with strings (text), numbers and storing these values in variables. In the next lesson we will learn how to output all that data to your screen with Python's print() function.

Previous: Variables