Python基本语法笔记

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#后面写注释

加上.0则自动作为float处理

输出int:

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

输出String:

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

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：

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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：

1	age = raw_input()

类型转换：

1	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：

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

import：

1 2	from sys import argv script, first, second, third = argv #将参数赋给这些变量

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.

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

str()可以转为string

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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." 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 list for number in the_count:     print "This is count %d" % number while i < 6:     print "At the top i is %d" % i     numbers.append(i)

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.