在类Unix系统上开始Python3编程入门

假设有个python脚本script.py，不管哪种Unix平台，都可以在命令行上通过解释器执行：

$ python script.py

Unix平台还可以在不明确指定python解释器的情况下，自动执行python解释器，这需要在python脚本的第一行添加如下shell魔术字符串：

#!/usr/bin/python

在#!之后写上python解释器的完整路径，通常在/usr/bin或/usr/local/bin目录下。还有一种方法是使用env这个命令，位于/bin或/usr/bin中，它会帮你在系统搜索路径中找到python解释器，python脚本的第一行就可以修改如下：

#!/usr/bin/env python

这样，执行python脚本时，就不必显式地调用python解释器了，只需要键入脚本的文件名即可：

$ script.py

在 Python 3 中接触的第一个很大的差异就是缩进是作为语法的一部分，这和C++等其他语言确实很不一样，所以要小心咯
缩进要使用4个空格（这不是必须的，但你最好这么做），缩进表示一个代码块的开始，非缩进表示一个代码的结束。没有明确的大括号、中括号、或者关键字。这意味着空白很重要，而且必须要是一致的。第一个没有缩进的行标记了代码块，意思是指函数，if 语句、 for 循环、 while 循环等等的结束。
不过这样的规定也使得 Python 程序写出来会更加美观，便于阅读，吐槽是没有用的，接受吧...o(╯□╰)o
Python 思想：
“一切都是对象！”
输入很简单

x = input("Please input x:")
Please input x:

在代码最后加上

input("Press Enter")

就可以让程序运行完后停一下

输出的 print 函数总结：
1. 字符串和数值类型
可以直接输出

>>> print(1)
1
>>> print("Hello World")
Hello World

2.变量
无论什么类型，数值，布尔，列表，字典...都可以直接输出

>>> x = 12
>>> print(x)
12
>>> s = 'Hello'
>>> print(s)
Hello
>>> L = [1,2,'a']
>>> print(L)
[1, 2, 'a']
>>> t = (1,2,'a')
>>> print(t)
(1, 2, 'a')
>>> d = {'a':1, 'b':2}
>>> print(d)
{'a': 1, 'b': 2}

3.格式化输出
类似于C中的 printf

>>> s
'Hello'
>>> x = len(s)
>>> print("The length of %s is %d" % (s,x))
The length of Hello is 5

看看《Python基础编程》中对格式化输出的总结：
(1). %字符：标记转换说明符的开始

(2). 转换标志：-表示左对齐；+表示在转换值之前要加上正负号；“”（空白字符）表示正数之前保留空格；0表示转换值若位数不够则用0填充

(3). 最小字段宽度：转换后的字符串至少应该具有该值指定的宽度。如果是*，则宽度会从值元组中读出。

(4). 点(.)后跟精度值：如果转换的是实数，精度值就表示出现在小数点后的位数。如果转换的是字符串，那么该数字就表示最大字段宽度。如果是*，那么精度将从元组中读出

(5).字符串格式化转换类型

转换类型 含义
d,i 带符号的十进制整数
o 不带符号的八进制
u 不带符号的十进制
x 不带符号的十六进制（小写）
X 不带符号的十六进制（大写）
e 科学计数法表示的浮点数（小写）
E 科学计数法表示的浮点数（大写）
f,F 十进制浮点数
g 如果指数大于-4或者小于精度值则和e相同，其他情况和f相同
G 如果指数大于-4或者小于精度值则和E相同，其他情况和F相同
C 单字符（接受整数或者单字符字符串）
r 字符串（使用repr转换任意python对象)
s 字符串（使用str转换任意python对象）

>>> pi = 3.141592653
>>> print('%10.3f' % pi) #字段宽10，精度3
  3.142
>>> print("pi = %.*f" % (3,pi)) #用*从后面的元组中读取字段宽度或精度
pi = 3.142
>>> print('%010.3f' % pi) #用0填充空白
000003.142
>>> print('%-10.3f' % pi) #左对齐
3.142
>>> print('%+f' % pi) #显示正负号
+3.141593

4.如何让 print 不换行
在Python中总是默认换行的

>>> for x in range(0,10):
 print(x)



0
1
2
3
4
5
6
7
8
9

如果想要不换行，之前的 2.x 版本可以这样 print x, 在末尾加上 ,
但在 3.x 中这样不起任何作用
要想换行你应该写成 print(x，end = '' )

>>> for x in range(0,10):
 print (x,end = '')



0123456789

拼接字符串：

>>> "Hello""World"
'HelloWorld'
>>> x = "Hello"
>>> y = "world"
>>> xy
Traceback (most recent call last):
 File "<pyshell#10>", line 1, in <module>
 xy
NameError: name 'xy' is not defined
>>> x+y
'Helloworld'

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