Python基本语法笔记

#后面写注释加上.0则自动作为float处理输出int:

print "He's %d pounds heavy." % my_weight

输出String:

print "He's got %s eyes and %s hair." % (my_eyes, my_hair)

print "." * 10  # what'd that do?..........

Use the %r for debugging, since it displays the "raw" data of the variable, but the others are used for displaying to users.单引号和双引号都可以用来表示字符串。%s可以输出中文（输出中文之前要在第一行加上#coding:utf-8）输出多行：

print """There's something going on here.With the three double-quotes.We'll be able to type as much as we like.Even 4 lines if we want, or 5, or 6."""

输入：

age = raw_input()

类型转换：

x = int(raw_input())

The input() function will try to convert things you enter as if they were Python code, but it has security problems so you should avoid it.输入之前先输出到屏幕：

age = raw_input("How old are you? ")

import：

from sys import argvscript, first, second, third = argv #将参数赋给这些变量

文件操作：

from sys import argvscript, filename = argvtxt = open(filename)print "Here's your file %r:" % filenameprinttxt.read()

常用文件操作函数：close -- Closes the file. Like File->Save.. in your editor.read -- Reads the contents of the file. You can assign the result to a variable.readline -- Reads just one line of a text file.truncate -- Empties the file. Watch out if you care about the file.write('stuff') -- Writes "stuff" to the file.输入参数：

# this one is like your scripts with argvdef print_two(*args):arg1, arg2 = argsprint "arg1: %r, arg2: %r" % (arg1, arg2)# ok, that *args is actually pointless, we can just do thisdef print_two_again(arg1, arg2):print "arg1: %r, arg2: %r" % (arg1, arg2)# this just takes one argumentdef print_one(arg1):print "arg1: %r" % arg1# this one takes no argumentsdef print_none():print "I got nothin'."

Truth Terms: and/or/not True Falsestr()可以转为stringif语句：

if cars > people:print "We should take the cars."elif cars < people:print "We should not take the cars."else:print "We can't decide."

List的使用：

def break_words(stuff):"""This function will break up words for us."""words = stuff.split(' ')return wordsdef sort_words(words):"""Sorts the words."""return sorted(words)def print_first_word(words):"""Prints the first word after popping it off."""word = words.pop(0)print worddef print_last_word(words):"""Prints the last word after popping it off."""word = words.pop(-1)print word

the_count = [1, 2, 3, 4, 5]fruits = ['apples', 'oranges', 'pears', 'apricots']change = [1, 'pennies', 2, 'dimes', 3, 'quarters']# this first kind of for-loop goes through a listfor number in the_count:print "This is count %d" % numberwhile i < 6:print "At the top i is %d" % inumbers.append(i)

注意事项：Every if-statement must have an else.If this else should never run because it doesn't make sense, then you must use a die function in the else that prints out an error message and dies, just like we did in the last exercise. This will find many errors.Never nest if-statements more than two deep and always try to do them one deep.Treat if-statements like paragraphs, where each if-elif-else grouping is like a set of sentences. Put blank lines before and after.Your boolean tests should be simple. If they are complex, move their calculations to variables earlier in your function and use a good name for the variable.Use a while-loop only to loop forever, and that means probably never. This only applies to Python; other languages are different.Use a for-loop for all other kinds of looping, especially if there is a fixed or limited number of things to loop over.