python loop详解_Python进阶学习笔记(3)-Loop

while

语法结构,用:隔开

while condition :

expression

x = 1

while x < 4 :

print(x)

x = x + 1

# Initialize offset

offset = 8

# Code the while loop

while offset != 0:

print("correcting...")

offset = offset-1

print(offset)

output

output:

correcting...

7

correcting...

6

correcting...

5

correcting...

4

correcting...

3

correcting...

2

correcting...

1

correcting...

0

while和if的混搭

# Initialize offset

offset = -6

# Code the while loop

while offset != 0 :

print("correcting...")

if offset > 0 :

offset = offset -1

else :

offset = offset + 1

print(offset)

for循环

List里的for循环

# areas list

areas = [11.25, 18.0, 20.0, 10.75, 9.50]

# Code the for loop

for i in areas :

print(i)

enumerate, 可以同时输出变量的序列和数值

l = ['Alice', 'Bob', 'Charlie']

for name in l:

print(name)

# Alice

# Bob

# Charlie

for i, name in enumerate(l):

print(i, name)

# 0 Alice

# 1 Bob

# 2 Charlie

默认是从0开始，可以指定从1或者从任意数字开始。

for i, name in enumerate(l, 1):

print(i, name)

# 1 Alice

# 2 Bob

# 3 Charlie

自定义输出格式

# areas list

areas = [11.25, 18.0, 20.0, 10.75, 9.50]

# Code the for loop

for index, area in enumerate(areas) :

print("room " + str(index+1) + ": " + str(area))

output

room 1: 11.25

room 2: 18.0

room 3: 20.0

room 4: 10.75

room 5: 9.5

双层list的for循环也是毫不费力

# house list of lists

house = [["hallway", 11.25],

["kitchen", 18.0],

["living room", 20.0],

["bedroom", 10.75],

["bathroom", 9.50]]

# Build a for loop from scratch

for x, y in house:

print("the " + str(x) + " is " + str(y) + " sqm" )

the hallway is 11.25 sqm

the kitchen is 18.0 sqm

the living room is 20.0 sqm

the bedroom is 10.75 sqm

the bathroom is 9.5 sqm

Dictionary里的for循环

和list不一样的是需要用到items()这个指令

# Definition of dictionary

europe = {'spain':'madrid', 'france':'paris', 'germany':'berlin',

'norway':'oslo', 'italy':'rome', 'poland':'warsaw', 'austria':'vienna' }

# Iterate over europe

for k, v in europe.items() :

print("the capital of " + k + " is " + v)

Numpy array里的for循环

numpy array可以是1D也可以是2D，1D的话和list一样，2D的话要用到np.nditer,把两列按照一列来显示。

# Import numpy as np

import numpy as np

# For loop over np_height

for x in np_height :

print(str(x) + " inches")

# For loop over np_baseball

for val in np.nditer(np_baseball) :

print(val)

Dataframe里的for循环

iterrows()按照行来分析。

# Import cars data

import pandas as pd

cars = pd.read_csv('cars.csv', index_col = 0)

cars.head()

# Iterate over rows of cars

for lab, row in cars.iterrows() :

print(lab)

print(row)

output

cars.head()

cars_per_cap country drives_right

US 809 United States True

AUS 731 Australia False

JPN 588 Japan False

IN 18 India False

RU 200 Russia True

output:

US

cars_per_cap 809

country United States

drives_right True

Name: US, dtype: object

AUS

cars_per_cap 731

country Australia

drives_right False

Name: AUS, dtype: object

JPN

cars_per_cap 588

country Japan

drives_right False

Name: JPN, dtype: object

IN

cars_per_cap 18

country India

drives_right False

Name: IN, dtype: object

RU

cars_per_cap 200

country Russia

drives_right True

Name: RU, dtype: object

MOR

cars_per_cap 70

country Morocco

drives_right True

Name: MOR, dtype: object

EG

cars_per_cap 45

country Egypt

drives_right True

Name: EG, dtype: object

两种方法添加列

# Import cars data

import pandas as pd

cars = pd.read_csv('cars.csv', index_col = 0)

cars.head()

# Code for loop that adds COUNTRY column

for lab, row in cars.iterrows():

cars.loc[lab,"COUNTRY"] = str.upper(row["country"])

# Print cars

print(cars)

2.apply

# Import cars data

import pandas as pd

cars = pd.read_csv('cars.csv', index_col = 0)

cars["country"]

# Use .apply(str.upper)

for lab, row in cars.iterrows() :

cars["COUNTRY"] = cars["country"].apply(str.upper)

print(cars)