Posted by In this post we’ll talk about python’s types, how to use them, how they’re treated, and what we can do with typing.
This is aimed at beginners who have heard the words “Python” and “Types” but haven’t quite nailed down what they have to do with each other.
This is Part 1 of a multi-part series on Python Typing.
Python’s Native Types
The best place to start is just by listing each of the types that Python uses natively so that way we can work through examples later. As with most core-python functionality, the best place to learn more is the documentation, specifically this page.
- Boolean –
bool - Integer –
int - Float –
float - Complex
- Iterator
- Generator
- List –
list - Tuple –
tuple - Range –
range - String –
str - Bytes
- Byte Array
- Memory View
- Set –
set - Frozenset –
frozenset - Dictionary –
dict - Context Manager
- Modules
- Functions
- Methods
- Code Objects
- Type Objects
- Null –
None - Ellipses
- NotImplemented
Whew, that’s a ton. Let’s focus on the more important ones for now.
Booleans
Truth values, these can take on one of two values – True or False.
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In [1]: type(True) Out[1]: bool In [2]: type(False) Out[2]: bool In [3]: type(5 == 5) Out[3]: bool In [4]: type(None is None) Out[4]: bool |
Integers
Basic numeric type, these are whole numbers.
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In [5]: type(5) Out[5]: int In [6]: type(6 * 10) Out[6]: int In [7]: type(-1) Out[7]: int |
Floats
Another numeric type, these are decimal numbers.
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In [8]: type(0.0) Out[8]: float In [9]: type(3.14159) Out[9]: float In [10]: type(2**3.1) Out[10]: float |
Lists
An ordered collection of items. These items don’t have to be the same type, and there’s no limit on the length of the
list. Lists are mutable, which we’ll talk about later.
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In [11]: type([1, 2, 3]) Out[11]: list In [12]: type([]) Out[12]: list |
Tuples
Another ordered collection of items, which also don’t have to be the same type, and there’s also no limit on the length.
However, the big difference between lists and tuples is that tuples are not mutable.
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In [13]: type((1, 2, 3)) Out[13]: tuple In [14]: type((1,)) Out[14]: tuple |
Ranges
Ranges are ordered sequences of numbers created with the range keyword.
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In [15]: list(range(0, 11, 2)) Out[15]: [0, 2, 4, 6, 8, 10] In [16]: type(range(10)) Out[16]: range In [17]: type(range(0, 11, 2)) Out[17]: range |
Strings
Strings are an ordered collection of “characters”.
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In [18]: type('a') Out[18]: str In [19]: type('this is a string') Out[19]: str |
Sets
Sets are an unordered collection of items. These are similar to lists, but are not mutable and not ordered.
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In [20]: type({1, 2, 3}) Out[20]: set |
Dictionaries
Dictionaries are mappings of Key to Value pairings. The keys can be any immutable thing, and the values can be
anything.
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In [21]: foo = {'a': 5, 'b': 10} In [22]: foo['a'] Out[22]: 5 In [23]: type(foo) Out[23]: dict In [24]: {[1, 2, 3]: 5} # can't have mutable keys --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-22-c0fedc33c691> in <module>() ----> 1 {[1, 2, 3]: 5} TypeError: unhashable type: 'list' |
None
The Null type, the type for something that doesn’t exist is called None.
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In [25]: type(None) Out[25]: NoneType |
Mutability
We mentioned mutability a lot, but didn’t nail down what that means. It’s a essentially just whether or not a variable
is “changeable”. For instance, with a mutable object (like a list) we can change the values in place.
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In [1]: foo = [1, 2, 3] In [2]: foo Out[2]: [1, 2, 3] In [3]: foo[0] = -5 In [4]: foo Out[4]: [-5, 2, 3] |
However an immutable object cannot be changed.
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In [5]: foo = (1, 2, 3) In [6]: foo Out[6]: (1, 2, 3) In [7]: foo[0] = -5 --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-7-c1a884884171> in <module>() ----> 1 foo[0] = -5 TypeError: 'tuple' object does not support item assignment |
Conclusion
Everything object in Python has a type, but above we went over the most basic and necessary ones.
In the next post we’ll talk about the types provided by the typing module in Python 3 and how they can be used.
Useful advice! I’m working on learning Python from a Matlab background, and types are something I’m struggling with.
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