Python快速入门（1）简介、函数、字符串

01

Python在Linux中的常用命令:

进入： python

#可以安装ipython,这样会自带代码提示功能

退出： exit()

进入Python命令行

清屏命令： ctrl + L

查看帮助 help() # ex. help(list)

Python提供内置函数实现进制转换：

bin()

hex()

02

Python文件类型：

1.源代码.py

通过下面的形式可直接运行.py文件：

在demo1.py的文件第一行加上：

#!/usr/bin/python

print 'hello,world'

然后给文件加上可执行型权限：

chmod +x demo1.py

现在可以通过如下形式执行py文件：

./demo1.py

2.字节代码

python源文件经编译后生成的扩展名为 .pyc 的文件

编译方法：

import py_compile

py_compile.compile("demo1.py")

---> 生成demo1.pyc

3.优化代码

经过优化的源文件，扩展名为 ".pyo"

>>>python -O -m py_compile demo1.py

生成demo1.pyo

Python程序示例：

#!/usr/bin/python
# import modules used here -- sys is a very standard one
import sys

# Gather our code in a main() function
def main():
print 'Hello there', sys.argv[1]
# Command line args are in sys.argv[1], sys.argv[2] ...
# sys.argv[0] is the script name itself and can be ignored

# Standard boilerplate to call the main() function to begin
# the program.
if __name__ == '__main__':
main()

运行这个程序：

$ ./hello.py Alice

Hello there Alice

函数：

# Defines a "repeat" function that takes 2 arguments.
def repeat(s, exclaim):
result = s + s + s # can also use "s * 3" which is faster (Why?)
#the reason being that * calculates the size of the resulting object once whereas with +, that calculation is made each time + is called
if exclaim:
result = result + '!!!'
return result

函数调用：

def main():
print repeat('Yay', False)      ## YayYayYay
print repeat('Woo Hoo', True)   ## Woo HooWoo HooWoo Hoo!!!

缩进：

Python使用4个空格作为缩进，具体可以参考如下文档：

see here: http://www.python.org/dev/peps/pep-0008/#indentation
03

Python变量

查看变量内存地址：id(var)

在线帮助技巧：

help(len) -- docs for the built in len function (note here you type "len" not "len()" which would be a call to the function)

help(sys) -- overview docs for the sys module (must do an "import sys" first)

dir(sys) -- dir() is like help() but just gives a quick list of the defined symbols

help(sys.exit) -- docs for the exit() function inside of sys

help('xyz'.split) -- it turns out that the module "str" contains the built-in string code, but if you did not know that, you can call help() just using an example of the sort of call you mean: here 'xyz'.foo meaning the
foo() method that runs on strings

help(list) -- docs for the built in "list" module

help(list.append) -- docs for the append() function in the list modul

04

运算符

raw_input() //从键盘获取值

ex.

a = raw_input("please input a:")

b = raw_input("please input b:")

05

数据类型

type() 可以查看某个字符的数据类型

三重引号：常用来做注释，函数中常用来做doc数据区

”“”

str

“”“

Python字符串：

Python strings are "immutable" which means they cannot be changed after they are created (Java strings also use this immutable style).

s = 'hi'
s = 'hi'
print s[1]          ## i
print len(s)        ## 2
print s + ' there'  ## hi there

#print在新行中进行打印
raw = r'this\t\n and that'   ## r'str' 表示声明的是一个原始字符串，将会原封不动的打印
print raw     ## this\t\n and that

multi = """It was the best of times.
It was the worst of times."""

pi = 3.14
##text = 'The value of pi is ' + pi      ## NO, does not work
text = 'The value of pi is '  + str(pi)  ## yes

字符串常用方法：

s.lower(), s.upper() #-- returns the lowercase or uppercase version of the string
s.strip() #-- returns a string with whitespace removed from the start and end
s.isalpha()/s.isdigit()/s.isspace()... #-- tests if all the string chars are in the various character classes
s.startswith('other'), s.endswith('other') #-- tests if the string starts or ends with the given other string
s.find('other') #-- searches for the given other string (not a regular expression) within s, and returns the first index where it begins or -1 if not found
s.replace('old', 'new') #-- returns a string where all occurrences of 'old' have been replaced by 'new'
s.split('delim') #-- returns a list of substrings separated by the given delimiter. The delimiter is not a regular expression, it's just text. 'aaa,bbb,ccc'.split(',') -> ['aaa', 'bbb', 'ccc']. As a convenient special case s.split() (with no arguments) splits on all whitespace chars.
s.join(list) #-- opposite of split(), joins the elements in the given list together using the string as the delimiter. e.g. '---'.join(['aaa', 'bbb', 'ccc']) -> aaa---bbb---ccc

更多内容可以参考如下文档：
http://docs.python.org/2/library/stdtypes.html#string-methods
字符串的格式化输出： % 运算符

# % operator
text = "%d little pigs come out or I'll %s and %s and %s" % (3, 'huff', 'puff', 'blow down')

#因为这行太长，可以用如下的方式：加括号
# add parens to make the long-line work:
text = ("%d little pigs come out or I'll %s and %s and %s" %
(3, 'huff', 'puff', 'blow down'))