python学习第三章：（变量、字符串、数、注释）-优快云博客

本文链接：https://blog.youkuaiyun.com/sambahong/article/details/145019782

2.1变量

2.1.1变量的命名和使用：（可以包含字母、数字、下划线）

1. message = "xxxxx" (√允许的)

2. _message = "xxxxx" (√)

3. 1_message = "xxxxx" (x不允许的) 不允许数字开头

4. 2message = "xxxxx" (x)

5. 0 = "xxxxx" (x)

6.如果变量名过长我们不允许有空格而是采取下划线的形式进行分割：longlong message(x)

longlong_message(√)

7.不要将python关键字和函数名用作变量(官方文档可看关键字函数名)：print = "xxxxx" (x)

2.2 字符串

2.2.1 表示方法

1.双引号表示手法："this is a string"

2.单引号表示手法：'this is a string'

3.双引号加单引号表示手法："The language 'Python'is named after Monty Python,not the snake."

2.2.2 使用“方法”来修改字符串的大小写

方法如下：

1. title()——首字母大写 2. upper()——全大写 3. lower()—— 全小写

xxx = "Hello python!!!!..."
print(xxx.lower())

message = "Hello python crash counrse world!!!"
print(message.upper())


xzw = "Hello world!!!"
print(xzw.title())

对应输出如下结果：

        hello python!!!!...
        HELLO PYTHON CRASH COUNRSE WORLD!!!
        Hello World!!!

2.2.3 在字符串中使用变量:(关于f字符串)

first_name = "xrz"
second_name = "and"
last_name = "xxy"

full_name = f"{first_name} {second_name} {last_name}"
print(full_name)

对应输出结果：

xrz and xxy

值得注意一点f字符串在3.6及之后版本才有，之前则需要采用format()

2.2.4 使用制表符或换行符来添加空白

print("python")
print("\tpython")

对应输出：

python
python

print("python")
print("\npython")

对应输出：

python

print("Languages:\n\tPython\n\tJava\n\tC++")

对应输出：一行中我们同时既可以用换行符也可以用制表符

Languages:
   Python
   Java
   C++

2.2.5 使用“方法”删除空白

方法如下：

1. rstrip()——删除右边的空白 2. lstrip()——删除左边的空白 3. strip()—— 删除左右的空白

del_r_languages = "python   "
print(del_r_languages.rstrip())


del_l_languages = "   python"
print(del_l_languages.lstrip())


del_s_languages = "   python   "
print(del_s_languages.strip())

对应输出：python（左右都无空格）

2.2.6 使用字符串时避免语法错误（灵活运用单引号双引号的表示手法）

'one of python's languages' (x)

"one of python's languages" (√)

2.3 数

3 + 2        //加
3 - 2        //减
2 * 3        //乘
3 / 2        //除
3 ** 2            //乘方运算，等于9
3 ** 3            //等于27
2 + 3 * 2        //满足数学运算规则，等于14
(2 + 3) * 2      //使用圆括号可以让python按照你指定的次序执行运算，等于12

关于整数和浮点数：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

2.3.1 同时给多个变量赋值

x,y,z = 0,1,2
print(x)
print(y)
print(z)

2.3.2 常量

常量类似于变量，但其值在程序的整个生命周期内保持不变。Python没有内置的常量类型，但Python程序员会使用全大写来指出应将某个变量视为常量，其值应始终不变：
MAX_CONNECTIONS = 5000
在代码中，要指出应将特定的变量视为常量，可将其字母全部大写。

2.4注释

在python中注释用#

#	xxx = "Hello python!!!!..."
#	print(xxx.lower())

python中的指导原则（我个人理解为是一种小彩蛋^^!）

import this #直接输入运行



#Beautiful is better than ugly.
#Explicit is better than implicit.
#Simple is better than complex.
#Complex is better than complicated.
#Flat is better than nested.
#Sparse is better than dense.
#Readability counts.
#Special cases aren't special enough to break the rules.
#Although practicality beats purity.
#Errors should never pass silently.
#Unless explicitly silenced.
#In the face of ambiguity, refuse the temptation to guess.
#There should be one-- and preferably only one --obvious way to do it.
#Although that way may not be obvious at first unless you're Dutch.
#Now is better than never.
#Although never is often better than *right* now.
#If the implementation is hard to explain, it's a bad idea.
#If the implementation is easy to explain, it may be a good idea.
#Namespaces are one honking great idea -- let's do more of those!

第二章完结散花...............明天要继续加油的呀！！

—————如有不足或错误望指出