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 argv script, first, second, third = argv #将参数赋给这些变量
文件操作：
from sys import argvscript, filename = argv txt = open(filename) print "Here's your file %r:" % filenameprint txt.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 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'."
Truth Terms: and/or/not True False
str()可以转为string
if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 words
def 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 word
def 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 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)
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.