Python基础知识学习笔记

学习的是python3.0往后的版本

打印hello world，单引号/双引号都可以，但是必须有括号

print('hello world')
print("hello world")

Python有5种数据类型

+加法运算 

有些浮点数数在计算机中是无法精确表示的，只能近似表示，因此用浮点数表示，会有精度损失，例如

算术运算符 

例子

引入模块

实际操作一下

关系运算符 

逻辑运算符

判断2019年是不是闰年

(2019%4==0 and 2019%100!=0) or (2019%400==0)

运算符的优先级

增量运算符

标识符规则 

输入 input

input函数

功能:读取键盘输入，将所有输入作为字符串看待

语法：input([prompt]),  [prompt]是提示符，最好提供

举例，可以看到，变量a是以字符串的形式存储在内存中的

a=input("in:")

输出print

 这个开头就知道了，现在考虑如何把多个变量输出到一行呢， 用逗号 ，

看个例子

选择分支结构 

score=68
gender="lady"
if score>=60:
    if gender=='lady':
        print("yes")
else:
    print('no')

多分支结构

score=68
if score>=90:
        print('A')
else:
    if score>=80:
        print('B')
    else:
        if score>=70:
            print('C')
        else:
            if score>=60:
                print('D')
            else:
                print('E')

其实python是有elif的，上面程序可以这样写，省的缩进会弄错

score=68
if score>=90:
    print('A')
elif score>=80:
    print('B')
elif score>=70:
    print('C')
elif score>=60:
    print('D')
else:
    print('E')

看了例子，判断篮球比分是否安全

 

points=int(input('Leading points:'))
have_ball=input('the leading team has ball:(yes/no)')
seconds=int(input('the remaining seconds:'))
points-=3

if have_ball=='yes':
    points+=0.5
else:
    points-=0.5

if points<0:
        points=0

points**=2

if points>seconds:
    print('safe')
else:
    print('not safe')

程序运行结果：

循环结构 

 while循环

c=0
while c<5:
    print('hello')
    c+=1

for循环

求e的值

 

e=1
factorial=1
for i in range(1,100):
    factorial*=i
    e+=1.0/factorial

print(e)

求pi的值

 

pi=0
sign=1
divisor=1
for i in range(1,10000000):
    pi+=sign/divisor
    sign*=-1
    divisor+=2
pi*=4
print('pi is:',pi)

 

n=27
for n in range(1,10):
    while n!=1:
        if n%2==0:
            n/=2
        else:
            n=n*3+1
        print(n)

求平方根

x=2
low=0.0
high=x
guess=(low+high)/2
while abs(guess**2-x)>1e-4:
    if guess**2>x:
        high=guess
    else:
        low=guess
    guess=(low+high)/2
print(guess)

判断素数

import math
n=10
for i in range(2,int(math.sqrt(n))+1):
    if n%i==0:
        print('the number is not a prime')
        break
else:
    print('the number is a prime')

 

打印前50个素数

 

import math
n=2
count=0
while count<50:
    for i in range(2,int(math.sqrt(n))+1):
        if n%i==0:
            break
    else:
        print(n)
        count+=1
    n+=1

判断回文数 

num=12321
num_p=0
num_t=num
while num!=0:
    num_p=num_p*10+num%10
    num=num/10

if num_t==num_p:
    print('ok')
else:
    print('no')

函数 

def sum(start,stop):
    sum=0
    for i in range(start,stop+1):
        sum+=i
    return sum

运行结果

global

x=1

def fun():
    global x
    x=2

fun()
print(x)

 

同时判断回文数和素数

 

num=121

def is_palin(num): 
    num_p=0
    num_t=num
    while num!=0:
        num_p=num_p*10+num%10
        num=num/10
     
    if num_t==num_p:
        return True
    else:
        return False   
    

def is_prime(num):
    for i in range(2,int(math.sqrt(n))+1):
        if n%i==0:
            return False
    else:
        return True

if is_palin(num) and is_prime(num):
    print('ok')
else:
    print('no')

打印月份日历

 

def is_leap_year(year):
    if year%4==0 and year%100!=0 or year%400==0:
        return True
    else:
        return False

def get_num_of_days_in_month(year,month):
    if month in (1,3,5,7,10,12):
        return 31
    elif month in(4,6,9,11):
        return 30
    elif is_leap_year(year):
        return 29
    else:
        return 28

def get_total_num_of_day(year,month):
    days=0
    for y in range(1800,year):
        if is_leap_year(y):
            days+=366
        else:
            days+=365
    for m in range(1,month):
        days+=get_num_of_days_in_month(m)

    return days
def get_start_day(year,month):
    return (3+get_total_num_of_day(year,month))%7

def get_month_english_name(month):
    if month==1:
        return 'January'
    elif month==2:
        return 'February'
    elif month==3:
        return 'March'
    elif month==4:
        return 'April'
    elif month==5:
        return 'May'
    elif month==6:
        return 'June'
    elif month==7:
        return 'July'
    elif month==8:
        return 'August'
    elif month==9:
        return 'September'
    elif month==10:
        return 'October'
    elif month==11:
        return 'November'
    else:
        return 'December'


year=2019
month=1
start_weekday=get_start_day(year,month)
print("%20s" %get_month_english_name(month),end=" ")
print("%10d" %year)
print("---------------------------------------------")
print("   Sun   Mon   Tue   Wed   Thu   Fri   Sat   ")
for i in range(0,start_weekday):
    print("      ",end="")
round=start_weekday
days_of_this_month=get_num_of_days_in_month(year,month)
for j in range(1,days_of_this_month+1):
        print("   %3d" %j,end="")
        round+=1
        if round%7==0:
            print("\n")
print("\n")

程序运行结果：

递归函数

阶乘

def p(n):
    if n==0 or n==1:
        return 1
    else:
        return n*p(n-1)

print(p(3))

斐波那契数列

 

def fib(n):
    if n==1 or n==2:
        return 1
    else:
        return fib(n-1)+fib(n-1)

print(fib(5))

汉诺塔

def hanoi(n,A,B,C):
    if n==1:
        print('Move',n,'from',A,'to',C)
    else:
        hanoi(n-1,A,C,B)
        print('Move',n,'from',A,'to',C)
        hanoi(n-1,B,A,C)

hanoi(4,'Lef','Mid','Right')