Python中隐藏的五种实用技巧分享

def my_awesome_function():
    ...

def my_awesome_function():
    Ellipsis

def my_awesome_function():
    pass

def my_awesome_function():
    "An empty, but also awesome function"

>>> import numpy as np
>>> array = np.arange(27).reshape(3, 3, 3)
>>> array
array([[[ 0, 1, 2],
        [ 3, 4, 5],
        [ 6, 7, 8]],

       [[ 9, 10, 11],
        [12, 13, 14],
        [15, 16, 17]],

       [[18, 19, 20],
        [21, 22, 23],
        [24, 25, 26]]])

>>> array[:, :, 1]
array([[ 1, 4, 7],
       [10, 13, 16],
       [19, 22, 25]])

>>> array[..., 1]
array([[ 1, 4, 7],
       [10, 13, 16],
       [19, 22, 25]])

>>> a, *b, c = range(1, 11)
>>> a
1
>>> c
10
>>> b
[2, 3, 4, 5, 6, 7, 8, 9]

>>> a, b, c = range(3)
>>> a
0
>>> b
1
>>> c
2

>>> lst = [1]
>>> a = lst[0]
>>> a
1
>>> (a, ) = lst
>>> a
1

>>> lst = [1]
>>> [a] = lst
>>> a
1

>>> l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
>>> flattened = [elem for sublist in l for elem in sublist]
>>> flattened
[1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> from functools import reduce
>>> reduce(lambda x,y: x+y, l)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> sum(l, [])
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> # 其实相当于 [] + [1, 2, 3] + [4, 5, 6] + [7, 8, 9]

>>> nums = [1, 3, 7]
>>> sum(nums)
11
>>> _
11
>>>

>>> 9 + _
20
>>> a = _
>>> a
20

found = False
a = 0

while a < 10:
    if a == 12:
        found = True
    a += 1
if not found:
    print("a was never found")

a = 0

while a < 10:
    if a == 12:
        break
    a += 1
else:
    print("a was never found")

In [13]: try:
    ...: {}['lala']
    ...: except KeyError:
    ...: print("Key is missing")
    ...: else:
    ...: print("Else here")
    ...:
Key is missing

In [14]: try:
    ...: {'lala': 'bla'}['lala']
    ...: except KeyError:
    ...: print("Key is missing")
    ...: else:
    ...: print("Else here")
    ...:
Else here