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: https://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：

https://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'))