這篇文章主要爲大家詳細介紹了python中list列表的高級函數,感興趣的小夥伴們可以參考一下
在Python所有的數據結構中,list具有重要地位,並且非常的方便,這篇文章主要是講解list列表的高級應用,基礎知識可以查看博客。
此文章爲python英文文檔的翻譯版本,你也可以查看英文版:https://docs.python.org/2/tutorial/datastructures.html
use a list as a stack: #像棧一樣使用列表
stack = [3, 4, 5]
stack.append(6)
stack.append(7)
stack
[3, 4, 5, 6, 7]
stack.pop() #刪除最後一個對象
7
stack
[3, 4, 5, 6]
stack.pop()
6
stack.pop()
5
stack
[3, 4]
use a list as a queue: #像隊列一樣使用列表
> from collections import deque #這裏需要使用模塊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'])
three built-in functions: 三個重要的內建函數
filter(), map(), and reduce().
1)、filter(function, sequence)::
按照function函數的規則在列表sequence中篩選數據
> def f(x): return x % 3 == 0 or x % 5 == 0
... #f函數爲定義整數對象x,x性質爲是3或5的倍數
> filter(f, range(2, 25)) #篩選
[3, 5, 6, 9, 10, 12, 15, 18, 20, 21, 24]
2)、map(function, sequence):
map函數實現按照function函數的規則對列表sequence做同樣的處理,
這裏sequence不侷限於列表,元組同樣也可。
> def cube(x): return x*x*x #這裏是立方計算 還可以使用 x**3的方法
...
> map(cube, range(1, 11)) #對列表的每個對象進行立方計算
[1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
注意:這裏的參數列表不是固定不變的,主要看自定義函數的參數個數,map函數可以變形爲:def func(x,y) map(func,sequence1,sequence2) 舉例:
seq = range(8) #定義一個列表
> def add(x, y): return x+y #自定義函數,有兩個形參
...
> map(add, seq, seq) #使用map函數,後兩個參數爲函數add對應的操作數,如果列表長度不一致會出現錯誤
[0, 2, 4, 6, 8, 10, 12, 14]
3)、reduce(function, sequence):
reduce函數功能是將sequence中數據,按照function函數操作,如 將列表第一個數與第二個數進行function操作,得到的結果和列表中下一個數據進行function操作,一直循環下去…
舉例:
def add(x,y): return x+y
...
reduce(add, range(1, 11))
55
List comprehensions:
這裏將介紹列表的幾個應用:
squares = [x**2 for x in range(10)]
#生成一個列表,列表是由列表range(10)生成的列表經過平方計算後的結果。
[(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)] 這裏是生成了一個列表,列表的每一項爲元組,每個元組是由x和y組成,x是由列表[1,2,3]提供,y來源於[3,1,4],並且滿足法則x!=y。
Nested List Comprehensions:
這裏比較難翻譯,就舉例說明一下吧:
matrix = [ #此處定義一個矩陣
... [1, 2, 3, 4],
... [5, 6, 7, 8],
... [9, 10, 11, 12],
... ]
[[row[i] for row in matrix] for i in range(4)]
#[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
這裏兩層嵌套比較麻煩,簡單講解一下:對矩陣matrix,for row in matrix來取出矩陣的每一行,row[i]爲取出每行列表中的第i個(下標),生成一個列表,然後i又是來源於for i in range(4) 這樣就生成了一個列表的列表。
The del statement:
刪除列表指定數據,舉例:
> a = [-1, 1, 66.25, 333, 333, 1234.5]
>del a[0] #刪除下標爲0的元素
>a
[1, 66.25, 333, 333, 1234.5]
>del a[2:4] #從列表中刪除下標爲2,3的元素
>a
[1, 66.25, 1234.5]
>del a[:] #全部刪除 效果同 del a
>a
[]
Sets: 集合
> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> fruit = set(basket) # create a set without duplicates
>>> fruit
set(['orange', 'pear', 'apple', 'banana'])
>>> 'orange' in fruit # fast membership testing
True
>>> 'crabgrass' in fruit
False
>>> # Demonstrate set operations on unique letters from two words
...
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a # unique letters in a
set(['a', 'r', 'b', 'c', 'd'])
>>> a - b # letters in a but not in b
set(['r', 'd', 'b'])
>>> a | b # letters in either a or b
set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'])
>>> a & b # letters in both a and b
set(['a', 'c'])
>>> a ^ b # letters in a or b but not both
set(['r', 'd', 'b', 'm', 'z', 'l'])
Dictionaries:字典
>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127 #相當於向字典中添加數據
>>> tel
{'sape': 4139, 'guido': 4127, 'jack': 4098}
>>> tel['jack'] #取數據
4098
>>> del tel['sape'] #刪除數據
>>> tel['irv'] = 4127 #修改數據
>>> tel
{'guido': 4127, 'irv': 4127, 'jack': 4098}
>>> tel.keys() #取字典的所有key值
['guido', 'irv', 'jack']
>>> 'guido' in tel #判斷元素的key是否在字典中
True
>>> tel.get('irv') #取數據
4127
也可以使用規則生成字典:
>>> {x: x**2 for x in (2, 4, 6)}
{2: 4, 4: 16, 6: 36}
enumerate():遍歷元素及下標
enumerate 函數用於遍歷序列中的元素以及它們的下標:
>>> for i, v in enumerate(['tic', 'tac', 'toe']):
... print i, v
...
0 tic
1 tac
2 toe
zip():
zip()是Python的一個內建函數,它接受一系列可迭代的對象作爲參數,將對象中對應的元素打包成一個個tuple(元組),然後返回由這些tuples組成的list(列表)。若傳入參數的長度不等,則返回list的長度和參數中長度最短的對象相同。利用*號操作符,可以將list unzip(解壓)。
>>> 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.
有關zip舉一個簡單點兒的例子:>>
> a = [1,2,3]
>>> b = [4,5,6]
>>> c = [4,5,6,7,8]
>>> zipped = zip(a,b)
[(1, 4), (2, 5), (3, 6)]
>>> zip(a,c)
[(1, 4), (2, 5), (3, 6)]
>>> zip(*zipped)
[(1, 2, 3), (4, 5, 6)]
reversed():反轉
>>> for i in reversed(xrange(1,10,2)):
... print i
...
sorted(): 排序
> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
> for f in sorted(set(basket)): #這裏使用了set函數
... print f
...
apple
banana
orange
pear
python的set和其他語言類似, 是一個 基本功能包括關係測試和消除重複元素.
To change a sequence you are iterating over while inside the loop (for example to duplicate certain items), it is recommended that you first make a copy. Looping over a sequence does not implicitly make a copy. The slice notation makes this especially convenient:
>>> words = ['cat', 'window', 'defenestrate']
>>> for w in words[:]: # Loop over a slice copy of the entire list.
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
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