2.1 测试环境

print (“Hello Python World!”)

2.2 变量

message = “Hello Python world!”
print(message)

message = “Hello python Crash Course world!”
print(message)

2.2.1 变量的命名和使用

变量的命名包含：字母数值下划线

正确的命名方式：

message = “xxxxxx”
_message = “xxxxxx”
greeting_message = “xxxxxx”

错误的命名方式：

1_message = “xxxxxx”

0 = “xxxxxx”

greeting message = “xxxxxx”

print = “xxxxxx” #不可以使用python的关键字和函数名

变量的命名应是简短有描述性的

student_name = “xxq”

s_n = “xxq”

2.2.2 使用变量时避免命名错误

message = “Hello Python world!”
print(mesage)

Traceback (most recent call last):

File “e:/project/python/2.1.py”, line 38, in

print(mesage)

NameError: name ‘mesage’ is not defined. Did you mean: ‘message’?

2.2.3 变量是盒子

student_name = “xxq”
print (student_name)

2.3 字符串

用引号括起来的都是字符串

string = “This is a string.”
print (string)
string = ‘This is also a string.’
print (string)

string = ‘I told my friend,”Python is my favorite language!”‘
print (string)

string = “The language ‘Python is named after Monty Python,not the snake.'”
print(string)

string = “One of Python’s strengths is its diverse and supportive community.”
print(string )

2.3.1 使用方法修改字符串的大小写

name = “ada lovelace”

print(name.title()) # .title() 首字母大写
print(name.upper()) # .upper() 所有字母大写

name1 = “ADA LOVELACE”

print(name1.lower()) # .lower() 所有字母小写

2.3.2 在字符串中使用变量

first_name = “ada”
last_name = “lovelace”

full_name = f”{first_name} {last_name}”
print(full_name)

f””方法出自3.6，python较前版本则使用 format()

将花括号内的变量替换为其值

2.3.3 使用制表符或换行符来添加空白

制表符

test = “Python”
print (test)

test = “/tPython”
print (test)

换行符

test = “Python”
print (test)
test = “/nPython”
print (test)

案例

test = “Languages:/nPython/nC/nJavascript”
print (test)

test = “Languages:/n/tPython/n/tC/n/tJavascript”
print (test)

2.3.4 删除空白

# .rstrip() 删除右边的空白

favorite_language = ‘Python ‘
print (favorite_language.rstrip())

# .lstrip() 删除左边的空白

favorite_language = ‘ Python’
print (favorite_language.lstrip())

# .strip() 删除左右两边的空白

favorite_language = ‘ Python ‘
print (favorite_language.strip())

2.3.5 使用字符串避免语法错误

错误案例

message = ‘One of Python’s strengths is its diverse community’
print (message)

修改后正确的案例

message = “One of Python’s strengths is its diverse community”
print (message)

2.4 数

# 加法

print (2 + 3)

# 减法

print (3- 2)

# 乘法

print (2 * 3)

# 除法

print (3 / 2)

print (4 / 2)

# 乘方运算

print (3 ** 2)

print (3 ** 3)

print (10 ** 6)

# 同一个表达式中使用多种运算

print (2 + 3 * 4)

print ((2 + 3) * 4)

2.4.2 浮点数

print (0.1 + 0.1)

print (0.2 + 0.2)

print (2 * 0.1)

print (2 * 0.2)

print (0.2 + 0.2)

2.4.3 整数和浮点数

print (4 / 2)

print (1 + 2.0)

print (2 * 3.0)

print (3.0 ** 2)

无论是那种运算，只要有操作数是浮点数，Python默认得到的总是浮点数

2.4.4 数中的下划线

这种表示使用于整数和浮点数，但只有 Python 3.6 和更高版本支持

universe_age = 14_000_000_000
print (universe_age)

2.4.5 同时个多个变量赋值

# 普通案例

x = 0
y = 1
z = 2

print (x)
print (y)
print (z)

# 同时个多个变量赋值（按循序）

x,y,z = 0,1,2