Python基础语法（2）——字典、函数定义使用、控制流（if&for&while）

7.3 字典Dictionary(键值对)

     创建字典：demoDic={"name":"Tom","age":10,"sex":1}

     查看key对应的Value值：demoDic["name"]

     删除字典中元素：del demoDic["name"]

     清空字典：demoDic.clear()

     向字典中插入新的元素：demoDic["school"]="XD"

     字典中元素可以是混合数据类型，且Key值不可变，Key元素可以为数字、字符串、元组(tuple)等，不能为List,字典中Key值必须唯一。

8 函数(Funciton)

8.1 函数定义声明

    不带参数及带参数的函数定义 

def say_hi():

    print("hi!")

say_hi()

say_hi()

def print_two_sum(a,b):

    print(a+b)

print_two_sum(3, 6)

def repeated_strings(str,times):

    repeateStrings=str*3

    return repeateStrings

getStrings=repeated_strings("hello ", 3)

print(getStrings)

在函数中声明全局变量使用global x

x=80

def foo():

    global x

    print("x is ",str(x))

    x=3

    print("x changed ",str(x))

foo()

print("x is ",str(x))

8.2 参数

默认参数:调用函数时，未给出参数值，此时使用默认参数

def repeated_string(string,times=1):

    repeated_strings=string*times

    return repeated_strings

print(repeated_string("hello "))

print(repeated_string("hello ",4))

默认参数之后的参数也必须是默认参数

关键字参数:在函数调用时，指明调用参数的关键字

def fun(a,b=3,c=6):

    print("a:"+str(a)+" b:"+str(b)+" c:"+str(c))

fun(1,4)

fun(10,c=8)

VarArgs参数:参数个数不确定情况下使用

带*参数为非关键字提供的参数

带**参数为含有关键字提供的参数

def func(fstr,*numbers,**strings):

    print("fstr:",fstr)

    print("numbers:",numbers)

    print("strings:",strings)

func("hello",1,2,3,str1="aaa",str2="bbb",str3=4)

9 控制流

9.1 if语句&for循环

if用法

num=36

guess=int(input("Enter a number:"))

if guess==num:

    print("You win!")

elif guess<num:

    print("The number you input is smaller to the true number!")

else:

    print("The number you input is bigger to the true number!")

print("Done")

for用法，其中range(1,10)为1-9的数字，不包含10

for i in range(1,10):

    print(i)

else:

    print("over")

且for对于List、Tupel以及Dictionary依然适用

a_list=[1,2,3,4,5]

for i in a_list:

    print(i)

   

b_tuple=(1,2,3,4,5)

for i in b_tuple:

    print(i)

c_dict={"Bob":15,"Tom":12,"Lucy":10}

for elen in c_dict:

    print(elen+":"+str(c_dict[elen]))

9.2 while循环

num=66

guess_flag=False

while guess_flag==False:

    guess=int(input("Enter an number:"))

    if guess==num:

        guess_flag=True

    elif guess<num:

        print("The number you input is smaller to the true number!")

    else:

        print("The number you input is bigger to the true number!")

print("You win!")

9.3 break&continue&pass 

num=66

while True:

    guess=int(input("Enter an number:"))

    if guess==num:

        print("you win!")

        break

    elif guess<num:

        print("The number you input is smaller to the true number!")

        continue

    else:

        print("The number you input is bigger to the true number!")

        continue

pass执行下一条语句，相当于什么都不做

a_list=[0,1,2]

print("using continue:")

for i in a_list:

    if not i:

        continue

    print(i)

print("using pass:")

for i in a_list:

    if not i:

        pass

    print(i)