一、 python笔记基础知识
1.Python打印输出
1 print("Hello Python")
2.算术运算符
# 加法运算符
1 print("4 + 2 =", 4+2)
输出:
4 + 2 = 6
# 减法运算符
1 print("4 - 2 =", 4-2)
输出:
4 - 2 = 2
# 乘法运算符
1 print("4 * 2 =", 4*2)
输出:
4 * 2 = 8
# 除法运算
1 print("4 / 2 =", 4/2)
输出:
4 / 2 = 2.0
# 除法取余
1 print("8 % 5 =", 8%5)
输出:
8 % 5 = 3
# 除法取整
1 print("8 // 5 =", 8//5)
输出:
8 // 5 = 1
# 幂运算
1 print("2 ** 3 =", 2**3)
输出:
2 ** 3 = 8
练习:求平均数
1 print("(2+3+2+4+5) / 5 =", (2+3+2+4+5) / 5)
输出:
(2+3+2+4+5) / 5 = 3.2
3.变量赋值
变量:在程序中存储计算结果,计算结果可变,通过变量名访问。
变量赋值:
1 a = 3 2 print("变量a=", a)
输出:
变量a= 3
a = 3 b = a print("变量b=", b) print("a和b的变量地址:",id(a), id(b))
输出:
a和b的变量地址: 1353988384 1353988384
变量赋值的另一种方式:
1 x, y, z = 1, 2, 3 2 print("x = %d, y = %d, z = %d" %(x, y, z))
输出:
x = 1, y = 2, z = 3
练习:变量和赋值运算练习
1 revenue = 1000 2 price = 20 3 car = revenue / price 4 print(car) 5 # 更新revenue的值 6 revenue = revenue + 500 7 car = revenue / price 8 print(car)
输出:
50.0
75.0
# 变量和赋值运算的另外一种方式
1 revenue += 500 2 print(revenue)
输出:2000
1 revenue -= 500 2 print(revenue)
输出:1500
4.整数和浮点数
# 整数
1 a = 8 2 print(type(a))
输出:
<class 'int'>
# 浮点数
a = 8.0
print(type(a))
输出:
<class 'float'>
注意:0.1是一个近似值
print(0.1 + 0.1 + 0.1)
输出:
0.30000000000000004
5.bool 运算符
print(1 < 2)
输出:
True
print(1 > 2)
输出:
False
print(1 <= 2)
输出:
True
print(1 >= 2)
输出:
False
print(1 == 1)
输出:
True
print(1 != 1)
输出:
False
print((1 < 2) and ( 1 > 2 ))
输出:
False
print((1 < 2) or (1 > 2))
输出:
True
# 翻转bool值
print(not 1 < 2)
输出:
False
6.字符串
# 单引号和双引号表示字符串
print("I am learning python") print('I am learning python')
# 查看字符串表示类型
str = ("I am learning python") print(type(str))
输出:
<class 'str'>
# 字符串拼接
First_word = "Hello" Secend_word = "World!" print(First_word + " " + Secend_word)
输出:
Hello World!
# 字符串重复输出
str = (First_word + " ") * 5
输出:
Hello Hello Hello Hello Hello
# 判断字符串长度
print(len(str))
输出:
30
练习:客户信息判断
give_name = "Luffy" middle_name = "D" family_name = "Monkey" name_length = len(give_name + middle_name + family_name) name_character_limit = 15 print(name_length <= name_character_limit)
输出:
True
7.数据类型和数据类型转换
# 数据类型
print(type(8))
输出:
<class 'int'>
print(type(8.0))
输出:
<class 'float'>
print(type(False))
输出:
<class 'bool'>
print(type(True))
输出:
<class 'bool'>
print(type("Hello"))
输出:
<class 'str'>
# 数据类型转换
print(float(8))
输出:
8.0
print(int(8.0))
输出:
8
print(int(True))
输出:
1
print(int(False))
输出:
0
print(float(True))
输出:
1.0
print(float(False))
输出:
0.0
print(type(int("8")))
输出:
<class 'int'>
print(type(float("8")))
<class 'float'>
8.字符串常见方法
# 获取字符串长度
print(len("Hello World!"))
输出:
12
# 获取字符串类型
print(type("Hello World!"))
输出:
<class 'str'>
# print 打印输出
print("Hello World!")
输出:
Hello World!
said = "Tom is a good boy" # 判断字符串是不是都是小写的 print(said.islower())
输出:
False
# 判断字母个数 print(said.count("o"))
输出:
4
# 查找字母在字符串中的位置 print(said.find("a"))
输出:
7