Python基础

基础数据类型

bool

z = 1 < 100
print(z)

True

type(z)

bool

string

print("Hello World" + "!")

Hello World!

hello_world = "Hello World"
hello_world[:5]

'Hello'

hello_world.split()

['Hello', 'World']

list

family = [1.80, 1.68, 1.2, 1.5]
family[0]

[1.8, 1.68]

max(family)

1.8

print(family.count(1.8))
family.append(1.8)
family

1

[1.8, 1.68, 1.2, 1.5, 1.8]

family.count(1.8)

2

# python list could contain different types...which is a mess to me
fam_height = ["father", 1.78, "mother", 1.68, "son", 1.80, "daughter", 1.65]
print(type(fam_height))

<class 'list'>

# slicing
# choose all
print(fam_height[:])
# first two
fam_height[:2]

['father', 1.78, 'mother', 1.68, 'son', 1.8, 'daughter', 1.65]

['father', 1.78]

# modification
fam_height[0:2] = ['lao wang', 1.77]
print(fam_height)

['lao wang', 1.77, 'mother', 1.68, 'son', 1.8, 'daughter', 1.65]

# append
fam_height = fam_height + ['second_son', 0.51]
print(fam_height)
fam_height.append('dau in law')
fam_height.append(170)
print(fam_height)

['lao wang', 1.77, 'mother', 1.68, 'son', 1.8, 'daughter', 1.65, 'second_son', 0.51]
['lao wang', 1.77, 'mother', 1.68, 'son', 1.8, 'daughter', 1.65, 'second_son', 0.51, 'dau in law', 170]

# delete
del(fam_height[6:8])
print(fam_height)

['lao wang', 1.77, 'mother', 1.68, 'son', 1.8, 'second_son', 0.51, 'dau in law', 170]

# locating the first one or error if not exist
print(fam_height.index(1.77))

1

# duplication
list_dup = ['a'] * 10
print(list_dup)

['a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a']

# iteration
for w in hello_world.split():
    print(w)

Hello
World

tuple

# unchangable
t = ('t', 'u', 'p', 'l', 'e')
# error if you want to change
# t[0] = 'd'
type(t)

tuple

# slicing
t[2:4]

('p', 'l')

# index
t.index('t')

0

dictionary

europe = {'spain':'madrid', 'france':'paris','germany':'berlin','italy':'rome'}
print(europe['germany'])

berlin

# show keys and values
europe.values()
europe.keys()
europe.items()

dict_items([('spain', 'madrid'), ('france', 'paris'), ('germany', 'berlin'), ('italy', 'rome')])

# 查找某个key的value
europe['france']

'paris'

# 这样更安全
europe.get('france')

'paris'

# 或者查找前，先判断key是否存在
'britain' in europe

False

# 还可以通过给定默认值，使不存在的查询也有返回值
europe.get('britain', 'unknown')

'unknown'

# 字典的增删改
europe['britain'] = 'london'
europe['britain'] = 'London'
del(europe['britain'])

# iteration
for country, capital in europe.items():
    print(country + "'s capital is " + capital)

spain's capital is madrid
france's capital is paris
germany's capital is berlin
italy's capital is rome

基础函数

help & ?

help(max)

Help on built-in function max in module builtins:

max(...)
    max(iterable, *[, default=obj, key=func]) -> value
    max(arg1, arg2, *args, *[, key=func]) -> value
    
    With a single iterable argument, return its biggest item. The
    default keyword-only argument specifies an object to return if
    the provided iterable is empty.
    With two or more arguments, return the largest argument.

?max

print

print("Hello World !")

Hello World !

weight = 60
height = 1.7
bmi = weight / height**2
print(bmi)

20.761245674740486

type 显示数据类型

type(weight)

int

type(bmi)

float

len

len(fam_height)

8

len(hello_world)

11

range

seq = range(0,9)
print(type(seq))
print(seq)
print(list(seq))

<class 'range'>
range(0, 9)
[0, 1, 2, 3, 4, 5, 6, 7, 8]

流程控制

if

x = 0
if x > 0 :
    print('x 是正数')
elif x < 0 :
    print('x 是负数')
else :   
    print('x 是 0')

x 是 0

for

family = [1.78, 1.68, 1.80, 1.65]
for height in family :
    print(height)

1.78
1.68
1.8
1.65

# get index with enumerate
for index, height in enumerate(family) :
    print('index ' + str(index) + ': ' + str(height))

index 0: 1.78
index 1: 1.68
index 2: 1.8
index 3: 1.65

while

# 计算 1..10的和
num = 1 # 循环开始前初始一个值num
sum = 0
while num <= 10:
    sum += num
    num = num + 1
print(sum)

55

函数

def fib(n):
    '''get a list of fibnacci series to n'''
    a, b = 0, 1
    result = []
    while a<n:
        result.append(a)
        a, b = b, a+b
    return result

fib(5)

[0, 1, 1, 2, 3]