《爱上Python 一日精通Python编程》Jamie Chan

第1章什么是Python?

Python——编程新手最好的选择

第2章为Python做好准备

#打印出单词"Hello World"
print("Hello World")
'''
这是注释
'''
print("Hello Python")

"""
这也是注释
"""

第3章变量和操作符的世界

3.1定义变量

userAge,userName = 16,'saber'
"""
相当于
userAge = 16
userName = 'saber'
"""

3.2命名变量

'''
与C一致:
1.字母数字下划线;
2.不能为关键字;
3.区分大小写;
命名规则举例:
1.驼峰式:ThisIsAVariableName
2.下划线式:this_is_a_variable_name
'''

3.3赋值符号

"""与C一致"""
"""注意区分 x=y 与 y=x 的不同"""

x = 8
y = 2
x = y
print("x =",x)
print("y =",y)

"""
运行结果:
x = 2
y = 2
"""

3.4基本操作符

+ - * / // % **
加法减法乘法除法整除求余指数

x = 5
y = 2
print("x+y =",x+y)
print("x-y =",x-y)
print("x*y =",x*y)
print("x/y =",x/y)
print("x//y =",x//y)    #向下取整
print("x%y =",x%y)
print("x**y =",x**y)
"""
运行结果:
x = 2
y = 2
x+y = 7
x-y = 3
x*y = 10
x/y = 2.5
x//y = 2
x%y = 1
x**y = 25
"""

3.5更多的分配操作符
+= -= *=

第4章 Pyhon中的数据类型

注释不能写在代码行的后面，会报语法错误。可跨行但开始时应独立成行书写。这一点与C不同。以上写法中，只有第三种正确。

但如果采用#的注释方法，则可以在代码行后直接注释。但此时并不支持跨行注释。

4.1整型——同C

4.2浮点型——同C

4.3字符串

[样例]
userName = 'peter',userSpouseName = "Janet",usrAge = '30'
a."" 或 '' 都可以,但必须配对使用，不能一个'一个"地使用
b.可以使用 + 连接多个字符串如: "I love"+" Saber"+" forever!" 等于 "I love Saber forever!"

print("I love"+" Saber"+" forever!")
"""[运行结果]:I love Saber forever!"""

4.3.1内建的字符串函数

'excalibur'.upper() #这是一条注释
"""将字符串中每一个字符都转化为大写"""

4.3.2使用%操作符格式化字符串

[格式]" string to be formatted " %(values or variables to be inserted into string,separated by commas)
a.引号内编写要格式化的字符串，写出% 使用一对小括号，括号内写上要插入字符串的值或变量。
b.这对包含值的小括号事实上叫做——元组
c.%d %f %s 宽度，保留小数位数等与C一致

brand = 'Apple'
exchangeRate = 1.235235344 
message = 'The price of this %s laptop is %d USD and the exchange rate is %4.2f USD to 1 EUR' %(brand,1299,exchangeRate)
print(message)
"""
[运行结果]The price of this Apple laptop is 1299 USD and the exchange rate is 1.24 USD to 1 EUR
"""

4.3.3使用format()方法格式化字符串
[格式]" string to be formatted ".format(values or variables to be inserted into string,separated by commas)
a.使用大括号，像这样:
message = 'The price of this {0:s} laptop is {1:d} USD and the exchange rate is {2:4.2f} USD to 1 EUR'.format("Apple",1299,1.4354351)
b.大括号内首先写下要使用参数的位置(从0开始)，后面加一个冒号(英文)，冒号后面写下格式化符号(d——整型 f——浮点型 s——字符串)，并且大括号内不能有任何空格。
c.如果不想要格式化字符串，可写为：
message = 'The price of this {} laptop is {} USD and the exchange rate is {} USD to 1 EUR'.format("Apple",1299,1.4354351)
那么，解释器将会根据大括号内所提供的变量顺序进行替换。

message = 'The price of this {0:s} laptop is {1:d} USD and the exchange rate is {2:4.2f} USD to 1 EUR'.format("Apple",1299,1.4354351)
print(message)
message = 'The price of this {} laptop is {} USD and the exchange rate is {} USD to 1 EUR'.format("Apple",1299,1.4354351)
print(message)


'''[运行结果]The price of this Apple laptop is 1299 USD and the exchange rate is 1.44 USD to 1 EUR
             The price of this Apple laptop is 1299 USD and the exchange rate is 1.4354351 USD to 1 EUR    '''

message1 = '{0} is easier than {1}'.format("Python",'Java')
message2 = '{1} is easier than {0}'.format("Python","Java")
message3 = '{:10.2f} and {:d}'.format(1.23454545,12)
message4 = '{}'.format(1.233455644)

print(message1)
print(message2)
print(message3)
print(message4)
"""[运行结果]
Python is easier than Java
Java is easier than Python
      1.23 and 12
1.233455644
"""

4.4Python中的类型转换

"""Python中的三个内建函数 int()   float()   str()  """

print(int(2.34))
print(int("4654"))
"""错误句 int("856.42")#ValueError: invalid literal for int() with base 10: '856.42' """
print(int(8)+6)
print(float(6+7))
print(float("85438.443"))
print(float("5"))
print(str(6))
print(str(9.56)+"dfjgh")
print(str("534fdf"))

"""[运行结果]
2
4654
14
13.0
85438.443
5.0
6
9.56dfjgh
534fdf
"""

4.5列表
""" a. 使用中括号[] """
""" b. 索引从0开始，最后一个元素为-1，倒数第二为-2 依此类推 """
""" c. 1:5叫做切片，它总是包括开始索引的元素，而不包括结尾索引的元素。因此，1:5表示从索引1到索引4 =（5-1） """
""" d. 切片第三个数字叫做步长 [1:5:2]从索引位置1~4=5-1 中每隔一个数字的子列表，故步长为2 """
""" e. 若不指定则默认:第一个数字为0，第二个数字为列表长度 [:4]表示0~3 [2:]表示2~4 （总长为5，共有5个元素）"""

myList = [1,2,3,4,5.5,"Hello"]

print(myList)
print(myList[2])
print(myList[-1])

myList2 = myList[1:5]
print(myList2)

myList[1] = 20
print(myList)

myList.append("How are you")
print(myList)

del myList[5]
print(myList)

4.6元组

"""值无法修改，初始化后值不会再变使用小括号() 其他类比列表"""

month = ("Jan","Feb","Mar")

4.7字典
""" 字典里的字是唯一的使用大括号{} """

userNameAndAge = {"peter":34,"John":42,"Saber":16,"Archer":"Not Available"}
userNameAndAge = dict(peter=34,John=42,Saber=16,Archer="Not Available")

第5章程序可交互

5.1&5.2 Input() Print()

myName = input("Please enter your name: ")
myAge = input("What about your age: ")
print("Hello World,my name is ",myName,"and I am",myAge,"years old.")

5.3三引号

print('''Hello World.
My name is John and
I am 20 years old.''')

5.4转义字符

print("a\tb\nc\\d\"e\'f")

第6章选择和判断

6.1条件语句

== != < > <= >= and or not

等于不等于小于大于小于等于大于等于与或非

6.2if语句

user = input("Enter 1 or 2:")

if user == "1":
    print("Hello World")
    print("How are you")
elif user == "2":
    print("Python Rocks")
    print("Ilove Python")
else:
    print("You didn't enter a valid number!")

6.3内联if

user = input("Enter 1 or 2:")
num=1 if user=="1" else 5
print(num)
print("This is task A " if user=="2" else "This is task B")

6.4for循环

6.4.1迭代

pets = ["cats","dogs","rabbits","hamsters"]
for mypets in pets:
    print(mypets)

for index,mypets in enumerate(pets):
    print(index,mypets)

message = "Hello"
for i in message:
    print(i)

6.4.2在一段数字上循环

range(start,end,step)

a.如不指定，start默认为0

b.如不指定，step默认为1，生成连续列表

c.end必须指定

range(5)生成[0,1,2,3,4]

range(3,10)生成[3,4,5,6,7,8,9]

range(4,10,2)生成[4,6,8]

for i in range(5):
    print(i)

6.5while循环

counter = 5
while counter>0:
    print("counter = ",counter)
    counter = counter - 1

6.6break中断

j = 0
for i in range(5):
    j=j+2
    print("i=",i,"j=",j)
    if(j==6):
        break

6.7continue

j = 0
for i in range(5):
    j=j+2
    print("i=",i,"j=",j)
    if(j==6):
        continue
    print("if counter!=6,print counter=",i)

6.8Try,Except

《爱上Python 一日精通Python编程》Jamie Chan

猜你喜欢