Variables

Variables (1)

A variable is a name for … something

• Something has a type

• … but its name hasn’t

>>> a = 42 >>> type(a) <class 'int'> >>> a = 1.5 >>> type(a) <class 'float'> >>> a = [42,'blah'] >>> type(a) <class 'list'>

Variables (2)

Python is a “dynamic language” (whatever that means)

• Names have no type

• Created when first assigned

• ⟶ Runtime error when accessed but not yet there

• … as opposed to compiled languages (whatever that means)

Naming rules: just like most other languages

• Start with Letters (Unicode since Python 3, ASCII in Python 2) or underscore

• Numbers in the following characters

• Case sensitive

Assignment Fun

Multiple assignments in one statement

a, b, c = 1, "Eins", 1.0
a, b = b, a  # "swap"

• Tuple unpacking

• Important concept throughout the entire language

• ⟶ later

Assignment has a value

a = b = c = 1

• Assignment is right associative

• ⟹ a, b, c are assigned 1

Assignment Details

More than one ever wants to know …

• Day-to-day programming does not need to know

• Good to know when something goes wrong

• Only valid for immutable types (int, float, str)

a = 42 b = a b = 7 Or equivalently …: a = 42 b = 42 b = 7