python 高级函数补充

# zip 案例
l1 = [1,2,3,4,5]
l2 = [11,22,33,44,55]

z = zip(l1, l2)

print(type(z))

for i in z:
    print(i)

<class 'zip'>

(1, 11)

(2, 22)

(3, 33)

(4, 44)

(5, 55)

l1 = ["wangwang", "mingyue", "yyt"]
l2 = [89, 23, 78]

z = zip(l1, l2)

for i in z:
    print(i)
   
l3 = (i for i in z)
print(l3)

('wangwang', 89)

('mingyue', 23)

('yyt', 78)

<generator object <genexpr> at 0x000001ED9F1F3ED0>

l1 = [11,22,33,44,55]

em = enumerate(l1)

l2 = [i for i in em]
print(l2)

[(0, 11), (1, 22), (2, 33), (3, 44), (4, 55)]

em = enumerate(l1, start=100)

l2 = [i for i in em]
print(l2)

[(100, 11), (101, 22), (102, 33), (103, 44), (104, 55)]

import collections
Point = collections.namedtuple("Point", ['x', 'y'])
p = Point(11, 22)
print(p.x)
print(p[0])

11

11

Circle = collections.namedtuple("Circle", ['x', 'y', 'r'])

c = Circle(100, 120, 20)
print(c)
print(type(c))

# 检测一下namedtuple到底属于谁的子类
isinstance(c, tuple)

Circle(x=100, y=120, r=20)

<class '__main__.Circle'>

True

import collections
help(collections.namedtuple)

Help on function namedtuple in module collections:

namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)

    Returns a new subclass of tuple with named fields.

    >>> Point = namedtuple('Point', ['x', 'y'])

    >>> Point.__doc__                   # docstring for the new class

    'Point(x, y)'

    >>> p = Point(11, y=22)             # instantiate with positional args or keywords

    >>> p[0] + p[1]                     # indexable like a plain tuple

    33

    >>> x, y = p                        # unpack like a regular tuple

    >>> x, y

    (11, 22)

    >>> p.x + p.y                       # fields also accessible by name

    33

    >>> d = p._asdict()                 # convert to a dictionary

    >>> d['x']

    11

    >>> Point(**d)                      # convert from a dictionary

    Point(x=11, y=22)

    >>> p._replace(x=100)               # _replace() is like str.replace() but targets named fields

    Point(x=100, y=22)

from collections import deque

q = deque(['a', 'b', 'c'])
print(q)

q.append('d')
print(q)

q.appendleft('x')
print(q)

deque(['a', 'b', 'c'])

deque(['a', 'b', 'c', 'd'])

deque(['x', 'a', 'b', 'c', 'd'])

d1 = {"one":1, "two":2, "three":3}
print(d1['one'])
print(d1['four'])

1

---------------------------------------------------------------------------

KeyError                                  Traceback (most recent call last)

<ipython-input-34-83fcfcbfcf65> in <module>

      1 d1 = {"one":1, "two":2, "three":3}

      2 print(d1['one'])

----> 3 print(d1['four'])

KeyError: 'four'

from collections import defaultdict
# lambda表达式，直接返回字符串
func = lambda: "ruochen"
d2 = defaultdict(func)

d2["one"] = 1
d2["two"] = 2

print(d2['one'])
print(d2['four'])

1

ruochen

from collections import Counter

# 为什么下面结果不把abcd...作为键值，而是以其中每一个字母作为键值
# 需要括号里内容为可迭代
c = Counter("abcdeabcabc")
print(c)

Counter({'a': 3, 'b': 3, 'c': 3, 'd': 1, 'e': 1})

# help(Counter)

s = {"I", "love", "you"}
c = Counter(s)

print(c)

Counter({'love': 1, 'you': 1, 'I': 1})