python数据分析实战-第2章-ptyhon世界简介

>>> 1 + 2
3
>>> (1.045 * 3)/4
0.78375
>>> 4 ** 2
16
>>> ((4 + 5j) * (2 + 3j))
(-7+22j)
>>> 4 < (2*3)
True
>>> a = 12 * 3.4
>>> a
40.8

>>> import math
>>> math.sin(a)
>>> from math import *
>>> sin(a)
>>> from math import sin

>>> dict = {‘name‘:‘William‘, ‘age‘:25, ‘city‘:‘London‘}
>>> dict["name"]
‘William‘
>>> for key, value in dict.items():
... print(key,value)
...
name William
city London
age 25

>>> list = [1,2,3,4]
>>> list
[1, 2, 3, 4]

>>> list[2]
3
>>> list[1:3]
[2, 3]
>>> list[-1]
4

>>> items = [1,2,3,4,5]
>>> for item in items:
... item + 1
...
23456

>>> items = [1,2,3,4,5]
>>> def inc(x): return x+1
...
>>> list(map(inc,items))
[2, 3, 4, 5, 6]

>>> list(map((lambda x: x+1),items))
[2, 3, 4, 5, 6]

filter函数只抽取函数返回结果为True的列表元素。
reduce函数对列表中的而所有元素依次计算过后返回唯一结果。
>>> list(filter((lambda x: x < 4), items))
[1, 2, 3]
>>> from functools import reduce
>>> reduce((lambda x,y: x/y), items)
0.008333333333333333

>>> S = [x**2 for x in range(5)]
>>> S
[0, 1, 4, 9, 16]

>>> a = 4
>>> if a > 3:
... if a < 5:
... print("I‘m four")
... else:
... print("I‘m a little number")
...
I‘m four
>>> if a > 3:
... if a < 5:
... print("I‘m four")
... else:
... print("I‘m a big number")
...
I‘m four