Iterator and Generator-2

lambda表达式

匿名函数

# lambda  params:expression
# params : 可选参数，逗号分割变量名
# expression：表达式，可以用条件语句，没有return或yield

# 用法：
    # 简单计算：lambda x: x*2
    # 添加条件： lambda x :True if x > 8 else False
    # 多个参数 lambda x, y : x+y
    # 用作排序： users.sort(key = lambda x(x[0], x[1]))
    # 默认字典：①defaultdic(lambda:0)
                # ② defaultdict(lambda:'bj')
                # ③ defaultdic(lambda :(0, 0))
    # 用作参数：① filter ② map
    # 要点：① 语法糖，用来创建函数对象  ② 表达式不要太复杂

f = lambda x :x*2

f(3)

6

f = lambda x : True if x > 8 else False  # 在if前面的是要返回的值

f(3)

False

f(9)

True

f = lambda x, y : x + y

f(8,9)

17

users = [('coop', 23), ('lilei', 26), ('hmm', 15), ('zhangsan', 40)]

users.sort(key=lambda x: (x[0],x[1])) # sort中有参数key，按照key的值进行排序，以x[0]
# 的值为key # 按照字母顺序排序x[0]指出了是coop,lilei,hmm等

users

[('coop', 23), ('hmm', 15), ('lilei', 26), ('zhangsan', 40)]

users.sort(key=lambda x:(x[1],x[0]))  # 按数字大小排序

users

[('hmm', 15), ('coop', 23), ('lilei', 26), ('zhangsan', 40)]

from collections import defaultdict

d = defaultdict(lambda :0)  # 默认赋值 等同于defaultdict(lambda:int)
只写出key，而没有指定value，默认从int中取值，即0，而不限与0

d['a']

0

d

defaultdict(<function __main__.<lambda>()>, {'a': 0})

d['b']

0

d

defaultdict(<function __main__.<lambda>()>, {'a': 0, 'b': 0})

d['c'] = 'coop'

d

defaultdict(<function __main__.<lambda>()>, {'a': 0, 'b': 0, 'c': 'coop'})

city = defaultdict(lambda : 'bj')

city

defaultdict(<function __main__.<lambda>()>, {})

city['shanghai']

'bj'

city

defaultdict(<function __main__.<lambda>()>, {'shanghai': 'bj'})

city['coop']

'bj'

city

defaultdict(<function __main__.<lambda>()>, {'shanghai': 'bj', 'coop': 'bj'})

point = defaultdict(lambda : (0, 0))

point[1]

(0, 0)

point[0]

(0, 0)

point['pp'] = (1,2)

point

defaultdict(<function __main__.<lambda>()>,
            {1: (0, 0), 0: (0, 0), 'pp': (1, 2)})

有些代码----一行搞定

# all(iterable)   Return True if all elements of the iterable are true (or if the iterable is empty). 都是真 
# any(iterable)Return True if any element of the iterable is true. If the iterable is empty, return False   任意
# min
# max
# sum
# reversed
# sorted
# zip  # 对应合并
# []列表  列表推到是
# ()生成器   生成器
# {k, v}    字典推倒
# set/{}    去重
# if 三元操作符   xx  if x else y
# enumerate   返回枚举，带索引

m = [1,2,3,0]

all(m)  # 可能是函数等
"""Signature: all(iterable, /)
Docstring:
Return True if bool(x) is True for all values x in the iterable
括号里面必须是可迭代的对象，如果可迭代对象里面的每一个都是True，则返回True
"""

False

m = [1,2,3,4,5]
all(m)

True

def f1():
    return True
def f2():
    return False
def f3():
    return True

all([f1(), f2(), f3()])  # [],可迭代的对象

False

# any

any([f1(), f2(), f3()])

True

m

[1, 2, 3, 4, 5]

min(m)

1

max(m)

5

sum(m)
"""Signature: sum(iterable, start=0, /)
Docstring:
Return the sum of a 'start' value (default: 0) plus an iterable of numbers
"""

"Signature: sum(iterable, start=0, /)\nDocstring:\nReturn the sum of a 'start' value (default: 0) plus an iterable of numbers\n"

sum(m)

15

reversed(m)
"""Init signature: reversed(self, /, *args, **kwargs)
Docstring:     
reversed(sequence) -> reverse iterator over values of the sequence

Return a reverse iterator"""

'Init signature: reversed(self, /, *args, **kwargs)\nDocstring:     \nreversed(sequence) -> reverse iterator over values of the sequence\n\nReturn a reverse iterator'

reversed(m)

<list_reverseiterator at 0x12fcd4c9d68>

for i in reversed(m):
    print(i)

5
4
3
2
1

[i for i in reversed(m)]

[5, 4, 3, 2, 1]

[i for i in reversed(range(8))]

[7, 6, 5, 4, 3, 2, 1, 0]

m

[1, 2, 3, 4, 5]

m = [2,3,90,5,4,34,22,55]
m.sort()

m

[2, 3, 4, 5, 22, 34, 55, 90]

m = [2,3,90,5,4,34,22,55]

sorted(m)

[2, 3, 4, 5, 22, 34, 55, 90]

sorted?
"""Signature: sorted(iterable, /, *, key=None, reverse=False)
Docstring:
Return a new list containing all items from the iterable in ascending order.

A custom key function can be supplied to customize the sort order, and the
reverse flag can be set to request the result in descending order.
Type:      builtin_function_or_method"""

m

[2, 3, 90, 5, 4, 34, 22, 55]

sorted(m, reverse=False)

[2, 3, 4, 5, 22, 34, 55, 90]

sorted(m, reverse=True)

[90, 55, 34, 22, 5, 4, 3, 2]

m1 = [-9,-3,-5,-7,3,4,6]

sorted(m1)

[-9, -7, -5, -3, 3, 4, 6]

sorted(m1, key = abs)

[-3, 3, 4, -5, 6, -7, -9]

zip?
"""Init signature: zip(self, /, *args, **kwargs)
Docstring:     
zip(iter1 [,iter2 [...]]) --> zip object

Return a zip object whose .__next__() method returns a tuple where
the i-th element comes from the i-th iterable argument.  The .__next__()
method continues until the shortest iterable in the argument sequence
is exhausted and then it raises StopIteration."""

x = [1,2,4,5,6,7,8]

y = ['q','b','c','d','e']

zip(x,y)

<zip at 0x12fcd3fc4c8>

print(zip(x,y))

<zip object at 0x0000012FCD4C6CC8>

print(list(zip(x,y)))

[(1, 'q'), (2, 'b'), (4, 'c'), (5, 'd'), (6, 'e')]

print(dict(zip(x,y)))

{1: 'q', 2: 'b', 4: 'c', 5: 'd', 6: 'e'}

name = ['coop','hmm','lilei']
city = ['beijing','shanghai','shenzhen']

dict(zip(name,city))

{'coop': 'beijing', 'hmm': 'shanghai', 'lilei': 'shenzhen'}

# 列表推导式
[i for i in range(10)]

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

[i^2 for i in range(10)]

[2, 3, 0, 1, 6, 7, 4, 5, 10, 11]

# 生成器表达式()
(x**3 for i in range(8))

<generator object <genexpr> at 0x0000012FCD4B73B8>

for y in (x**3 for x in range(8)):
    print(y)

0
1
8
27
64
125
216
343

# 字典推导式
info = dict(zip(name, city))

info

{'coop': 'beijing', 'hmm': 'shanghai', 'lilei': 'shenzhen'}

info_new = {}
for k, v in info.items():
    info_new[k] = v.upper()
print(info_new)

{'coop': 'BEIJING', 'hmm': 'SHANGHAI', 'lilei': 'SHENZHEN'}

{k:v.upper() for k, v in info.items()}  # 与上面同样的效果

{'coop': 'BEIJING', 'hmm': 'SHANGHAI', 'lilei': 'SHENZHEN'}

# 去重set
s = [1,1,2,3,4,5,4,5,64,6,4,3,6]

set(s)

{1, 2, 3, 4, 5, 6, 64}

s

[1, 1, 2, 3, 4, 5, 4, 5, 64, 6, 4, 3, 6]

list(set(s))

[64, 1, 2, 3, 4, 5, 6]

三元操作符

if True:
    pass
else:
    pass

True if s =='a' else False

False

s

[1, 1, 2, 3, 4, 5, 4, 5, 64, 6, 4, 3, 6]

s = 'a'

True if  s =='a' else False 

True