基礎語法

1.變量

1.1變量作用

變量是用于存儲數據

1.2變量定義規范

聲明變量

name = "vita"
pep8規范：等號兩邊要有空格

變量定義規則

• 變量名只能是字母、數字、下劃線的任意組合
• 變量名的第一個字符不能是數字
• 程序關鍵字不能是數字，例如if else while等

變量命名習慣

駝峰體
AgeOfVita = 27
下劃線
age_of_vita = 27

變量定義的low方式

變量名為中文、拼音 名字 = "vita"
變量名過長 qeqweqwe_qweqweqw_qwewqeq
變量名詞不達意 a = 23

1.3常量

常量定義

常量即指不變的量，如pai 3.1415926 ,或在程序運行過程中不會改變的量。
Python中沒有專門的語法定義常量，程序員約定用變量名全部大寫代表常量。
python中可自定義一個不修改的常量的類。

AGE_OF_VITA = 27

Java中定義常量，修改該常量會報錯

public static final String SUNDAY = "SUNDAY";

c語言中定義常量，修改該常量也會報錯

const int count = 60;

變量與常量用法示例

在使用中變量和常量沒什么區別

Python 2.7.16 (v2.7.16:413a49145e, Mar  4 2019, 01:37:19) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license()" for more information.
>>> a = 1
>>> b = a
>>> print(a)
1
>>> print(b)
1
>>> a=2
>>> print(a)
2
>>> print(b)
1
>>> 
>>> 
>>> A = 10
>>> B=A
>>> print(A)
10
>>> print(B)
10
>>> A=20
>>> print(A)
20
>>> print(B)
10
>>> 

2.讀取用戶輸入

name = input("please input your name:")
age = input("please input your age:")
hometown = input("please input your hometown:")
print("your name is:"+name
      + " your age is:"+age
      + " your hometown is:"+hometown)

運行
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
please input your name:vita
please input your age:27
please input your hometown:jl
your name is:vita your age is:27 your hometown is:jl

3.注釋

本行注釋

age = input("please input your age:")    # age pep8規范：#號前面至少兩個空格，后面一個空格

單行注釋

hometown = input("please input your hometown:")
# print age pep8規范：#號前面無空格，后面一個空格

多行注釋

"""
print age 
name hometown
"""
'''
print age 
name hometown
pep8規范：注釋與下面的代碼的空行不能多于兩行
'''

print("your name is:"+name
      + " your age is:"+age
      + " your hometown is:"+hometown)

4.數據類型

4.1數字類型

4.1.1介紹

int(整型)

在32位機器上，整數的位數為32位，取值范圍為-2**31~2**31 -1，即-2147483648~214748364
在64位系統上，整數的位數為64位，取值范圍為-2**63~2**63-1,即-9223372036854775808~9223372036854775807

long(長整型)

跟C語言不同，Python的長整型沒有指定寬度，即python沒有限制長整數數值的大小，但實際上由于內存的限制，我們使用的長整數數值不可能無限大。

注意：

自從Python2.2起，如果整數發生溢出，Python會自動把int轉換為long，所以現在在long數據后面不加字母L也不會導致嚴重后果了。
在Python3中沒有int和long的區分了，全部都是int

除了int和long外，還有float浮點型，復數型

4.1.2Python2&3之int long

 (venvP3) E:\PythonProject\python-test>python2
Python 2.7.16 (v2.7.16:413a49145e, Mar  4 2019, 01:37:19) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> type(2**4)
<type 'int'>
>>> type(2**65)
<type 'long'>
>>> quit()

(venvP3) E:\PythonProject\python-test>python3
Python 3.6.2 (v3.6.2:5fd33b5, Jul  8 2017, 04:57:36) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> type(2**4)
<class 'int'>
>>> type(2**65)
<class 'int'>
>>>

4.2字符串

在Python中，加了引號的字符就被認為是字符串

4.2.1字符串種類

Name = "vita"   # 雙引號
Age = "27"  # age是字符串
AgeNum = 27  # age是int
Msg = 'My name is vita,i am 27 years old!'  # 一對單引號
# 一對三個單引號
MsgThree = '''
My name is vita,
i am 27 years old!
'''
# 三個雙引號
MsgDouThree = """
My name is vita,
i am 27 years old!
""" 

4.2.2單引號，雙引號，多引號的區別

單引號和雙引號沒有任何區別，只是在下面情況下需要考慮單雙引號配合

Msg = "my name is vita,I'm 27 years old"

多引號的作用是多行字符串，需要使用多引號

# 一對三個單引號
MsgThree = '''
My name is vita,
i am 27 years old!
'''
# 三個雙引號
MsgDouThree = """
My name is vita,
i am 27 years old!
"""

4.2.3字符串拼接

字符串可以進行“相加”和“相乘”運算

>>> name = "vita"
>>> age = "27"
>>> print("your name is:"+name+" your age is:"+age)
your name is:vita your age is:27
>>> print("v"*3)
vvv

字符串不能喝整數拼接

>>> name = "vita"
>>> age = 27
>>> print(name+age)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must be str, not int

4.3布爾型

布爾型就兩個值，true和false，主要用于邏輯判斷

>>> a =3
>>> b = 5
>>> a>b
False
>>> a<b
True

4.4格式化輸出

name = input("input your name:")
age = input("input your age:")
hometown = input("input your hometown:")
msg = '''
------the info of %s is ------
name:       %s
age:        %s
hometown:   %s
------the info of end   ------
''' % (name, name, age, hometown)
print(msg)

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
input your name:vita
input your age:27
input your hometown:jl

------the info of vita is ------
name:       vita
age:        27
hometown:   jl
------the info of end   ------

4.5運算符

運算符種類算數運算符、比較運算符、邏輯運算符、賦值運算符

>>> a = 3
>>> b = 4
>>> a>b and a==3
False
>>> a<b and a==3
True

>>> a<b or a!=3
True
>>> a>b or a==3
True

>>> not a==3
False
>>>

4.6流程控制

4.6.1單分支

if 條件成立:
    執行代碼

# _*_coding:utf-8_*_
"""
輸入姓名，性別和年齡，
如果是女生且年齡小于28，輸出我喜歡年輕女孩
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()讀入的age是字符串，要轉換為int才能與28做大小比較
age = int(input("input your age:"))
if sex.lower() == "girl" and age < 28:
    print(name+" i like young girl")

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):GIRL
input your age:26
vita i like young girl

4.6.2雙分支

if 條件:
    條件滿足，執行代碼
else:
    條件不滿足，執行代碼

# _*_coding:utf-8_*_
"""
輸入姓名，性別和年齡，
如果是女生
年齡小于28，輸出我喜歡年輕女孩,
年齡不小于28，輸出年齡比我大也可以
如果不是女生
輸出我不喜歡男生
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()讀入的age是字符串，要轉換為int才能與28做大小比較
age = int(input("input your age:"))
if sex.lower() == "girl" :
    if age < 28:
        print(name+" i like young girl")
    else:
        print("the age is greater than me is also ok!")
else:
    print("i do not like boy")

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):girl
input your age:12
vita i like young girl

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):girl
input your age:28
the age is greater than me is also ok!

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):boy
input your age:23
i do not like boy

4.6.3多分支

if 條件:
    滿足條件執行代碼
elif 條件:
    上面條件不滿足，執行這里
elif 條件:
    上面條件不滿足，執行這里
else:
    所有條件都不滿足，執行這里

# _*_coding:utf-8_*_
"""
輸入姓名，性別和年齡，
如果是女生
年齡小于28，輸出我喜歡年輕女孩,
年齡不小于28，輸出年齡比我大也可以
如果不是女生
輸出我不喜歡男生
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()讀入的age是字符串，要轉換為int才能與28做大小比較
age = int(input("input your age:"))
if sex.lower() == "girl" :
    if age < 28:
        print(name+" i like young girl")
    else:
        print("the age is greater than me is also ok!")
elif sex.lower() == "boy":
    print("i do not like boy")
else:
    print("your input is not manual human")

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):w
input your age:23
your input is not manual human

4.6.4while

while 條件:
    執行代碼

"""
只打印1-10的偶數
"""
count = 0
while count < 10:
    if count%2 == 0:
        print(count)
    count = count + 1

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
2
4
6
8

"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
    if count == 5:
        pass
    elif count>=6 and count<=8:
        print(count*count)
    else:
        print(count)
    count = count + 1

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4
36
49
64
9
10

4.6.5死循環(dead loop)

只要運行起來，就不再停止,直到把內存耗盡

"""
只打印1-10的偶數
"""
count = 0
while count < 10:
    print(count)
    # count = count + 1
        #注釋掉最后一行，程序一直成立，會一直運行

4.6.6循環終止

break:用于完全結束一個循環，跳出循環體執行循環后面的語句
continue:終止本次循環，下次的循環繼續

"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
    if count == 5:
        # 這里一定要記得把count+1,否則count就一直等于5，就死循環了
        count = count + 1
        continue
    elif count>=6 and count<=8:
        print(count*count)
    else:
        print(count)
    count = count + 1

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4
36
49
64
9
10

"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
    if count == 5:
        # 這里一定要記得把count+1,否則count就一直等于5，就死循環了
        count = count + 1
        break
    elif count>=6 and count<=8:
        print(count*count)
    else:
        print(count)
    count = count + 1

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4

4.6.7while...else

只有在Python中有while...else
while后面的else指，當while循環正常執行完，中間沒有被break中止的話，就會執行else

count = 0
while count <= 3:
    if count == 2:
        count = count + 1
        continue
    else:
        print(count)
    count = count + 1
else:
    print("success")

        E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
3
success

count = 0
while count <= 3:
    if count == 2:
        count = count + 1
        break
    else:
        print(count)
    count = count + 1
else:
    print("success")

        E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1

本章代碼案例：

"""
猜年齡游戲：
允許用戶最多猜三次，猜了三次后，詢問是都繼續玩，如果輸入Y，可以繼續猜三次，否則退出
"""
age = 23
count = 0
while count < 3:
    try:
        guess_age = int(input("input the age of you think:"))
    except ValueError:
        print("you should input one number!")
        count = count + 1
        continue

    if guess_age > 23:
        print("the age you input is too big!")
    elif guess_age < 23:
        print("the age you input is too small!")
    else:
        print("excellent!you are right!")
        break
    count = count + 1
    while count == 3:
        your_choice = input("you only have three chances,would you like to continue(Y|y/N|n):")
        if your_choice.lower() == "y":
            count = 0
        elif your_choice.lower() =="n":
            break
        else:
            print("your input is illegal!input again!")

運行

E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/guessage.py
input the age of you think:2
the age you input is too small!
input the age of you think:45
the age you input is too big!
input the age of you think:33
the age you input is too big!
you only have three chances,would you like to continue(Y|y/N|n):y
input the age of you think:2w
you should input one number!
input the age of you think:24
the age you input is too big!
input the age of you think:55
the age you input is too big!
you only have three chances,would you like to continue(Y|y/N|n):y
input the age of you think:23
excellent!you are right!

Process finished with exit code 0