Whether it's doing scientific computing or writing applications , You need to use some basic data structures , Such as the list , Tuples , Dictionary, etc .
This article will explain in detail Python These basic data structures in .
The list is list, It can be expressed in square brackets ：
In [40]: ages = [ 10, 14, 18, 20 ,25] In [41]: ages Out[41]: [10, 14, 18, 20, 25]
list There are some very useful ways , such as append,extend,insert,remove,pop,index,count,sort,reverse,copy etc. .
for instance ：
>>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']
>>> fruits.count('apple')
2
>>> fruits.count('tangerine')
0
>>> fruits.index('banana')
3
>>> fruits.index('banana', 4) # Find next banana starting a position 4
6
>>> fruits.reverse()
>>> fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']
>>> fruits.append('grape')
>>> fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']
>>> fruits.sort()
>>> fruits
['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']
>>> fruits.pop()
'pear'The stack is characterized by last in, first out , And the list gives us append and pop Method , So it's very easy to use lists to implement stacks ：
>>> stack = [3, 4, 5] >>> stack.append(6) >>> stack.append(7) >>> stack [3, 4, 5, 6, 7] >>> stack.pop() 7 >>> stack [3, 4, 5, 6] >>> stack.pop() 6 >>> stack.pop() 5 >>> stack [3, 4]
The queue is characterized by first in, first out , But using lists to insert elements at the head of a queue is slow , Because you need to move all the elements .
We can use collections.deque To quickly operate from both ends ：
>>> from collections import deque
>>> queue = deque(["Eric", "John", "Michael"])
>>> queue.append("Terry") # Terry arrives
>>> queue.append("Graham") # Graham arrives
>>> queue.popleft() # The first to arrive now leaves
'Eric'
>>> queue.popleft() # The second to arrive now leaves
'John'
>>> queue # Remaining queue in order of arrival
deque(['Michael', 'Terry', 'Graham'])To create a list , The usual practice is to use for loop , To traverse the list , And set a value for it ：
>>> squares = [] >>> for x in range(10): ... squares.append(x**2) ... >>> squares [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
Or we can use list derivation to generate lists more concisely ：
squares = [x**2 for x in range(10)]
The structure of list derivation is the following content contained in a square bracket ： An expression , Followed by a for Clause , Then there are zero or more for or if Clause .
The list derivation will traverse for The elements of a sentence , And use expressions to evaluate , Return the generated element as a new list element .
Look at a more complicated ：
>>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y] [(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]
The above expression is equivalent to ：
>>> combs = [] >>> for x in [1,2,3]: ... for y in [3,1,4]: ... if x != y: ... combs.append((x, y)) ... >>> combs [(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]
List derivations can also be nested , If we have a matrix ：
>>> matrix = [ ... [1, 2, 3, 4], ... [5, 6, 7, 8], ... [9, 10, 11, 12], ... ]
You can use the following expression to exchange the matrix between rows and columns ：
>>> [[row[i] for row in matrix] for i in range(4)] [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
Or use a simpler one zip function ：
>>> list(zip(*matrix)) [(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]
To delete an element from a list, you can use del.del You can delete a specific value from the list , You can also delete slices , Even delete the entire list ：
>>> a = [-1, 1, 66.25, 333, 333, 1234.5] >>> del a[0] >>> a [1, 66.25, 333, 333, 1234.5] >>> del a[2:4] >>> a [1, 66.25, 1234.5] >>> del a[:] >>> a [] >>> del a
Tuples are very similar to lists , The difference is that tuples are immutable .
Tuples are represented by parentheses , Or you don't have to use parentheses .
>>> t = 12345, 54321, 'hello!' >>> t[0] 12345 >>> t (12345, 54321, 'hello!') >>> # Tuples may be nested: ... u = t, (1, 2, 3, 4, 5) >>> u ((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
Tuples and List It's very similar to , There are slicing and indexing operations .
Tuples can be easily unpacked ：
>>> x, y, z = t
Use together set Functions or curly braces .
The elements in a collection are not repetitive , This point is related to java Medium set Is very similar .
Because the dictionary representation is also curly braces , So if you need to create an empty collection , Need to use set, Because it's empty {} It's a dictionary .
Look at some simple examples of collections ：
>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
>>> print(basket) # show that duplicates have been removed
{'orange', 'banana', 'pear', 'apple'}
>>> 'orange' in basket # fast membership testing
True
>>> 'crabgrass' in basket
False
>>> # Demonstrate set operations on unique letters from two words
...
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a # unique letters in a
{'a', 'r', 'b', 'c', 'd'}
>>> a - b # letters in a but not in b
{'r', 'd', 'b'}
>>> a | b # letters in a or b or both
{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
>>> a & b # letters in both a and b
{'a', 'c'}
>>> a ^ b # letters in a or b but not both
{'r', 'd', 'b', 'm', 'z', 'l'}Just like the list , Sets also support derivation ：
>>> a = {x for x in 'abracadabra' if x not in 'abc'}
>>> a
{'r', 'd'}Dictionaries are also represented by curly braces , The difference is that the elements in the dictionary are based on key:value In the form of .
Here are some basic operations of the dictionary ：
>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> tel
{'jack': 4098, 'sape': 4139, 'guido': 4127}
>>> tel['jack']
4098
>>> del tel['sape']
>>> tel['irv'] = 4127
>>> tel
{'jack': 4098, 'guido': 4127, 'irv': 4127}
>>> list(tel)
['jack', 'guido', 'irv']
>>> sorted(tel)
['guido', 'irv', 'jack']
>>> 'guido' in tel
True
>>> 'jack' not in tel
FalseExcept for the curly brackets , You can also use dict Function to build a dictionary ：
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
{'sape': 4139, 'guido': 4127, 'jack': 4098}If the keyword is a simple character , You can write this directly ：
>>> dict(sape=4139, guido=4127, jack=4098)
{'sape': 4139, 'guido': 4127, 'jack': 4098}The same derivation can be used ：
>>> {x: x**2 for x in (2, 4, 6)}
{2: 4, 4: 16, 6: 36}We usually use for Statement to traverse a collection or dictionary ,list etc. .
When we traverse the dictionary , have access to items() Method to get key and value：
>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
... print(k, v)
...
gallahad the pure
robin the braveIf it's a list , Then you can use enumerate Function to get index and value：
>>> for i, v in enumerate(['tic', 'tac', 'toe']): ... print(i, v) ... 0 tic 1 tac 2 toe
We used it before zip function ,zip Function can match elements in multiple sequences one by one ：
>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
... print('What is your {0}? It is {1}.'.format(q, a))
...
What is your name? It is lancelot.
What is your quest? It is the holy grail.
What is your favorite color? It is blue.This article has been included in http://www.flydean.com/06-python-data-structure/ The most popular interpretation , The deepest dry goods , The most concise tutorial , There are so many tricks you don't know about waiting for you to discover ！ Welcome to my official account. :「 Program those things 」, Know technology , Know you better ！
