python入门 -- 学习笔记2

习题11：提问

　　--  接受键盘的输入  raw_input

　　input() 和 raw_input() 有何不同？
　　input() 函数会把你输入的东西当做 Python 代码进行处理，这么做会有安全问题，你应该避开
这个函数。

代码：

print "how old are you?",

age = raw_input()
print "How tail are you?",
height = raw_input()
print "how much do you weight?",
weight = raw_input()

print "So, you're %r old, %r tall and %r heavy." % (
　　age, height, weight)

结果：

习题12：提示别人

代码：

age = raw_input("How old are you? ")
height = raw_input("How tall are you? ")
weight = raw_input("How much do you weight? ")

print "So, you're %r old, %r tall and %r heavy." % (age, height, weight)

结果：

习题13：参数、解包、变量

　　--   将变量传递给脚本的方法(所谓脚本，就是你写的 .py 程序)，涉及“参数”

　　--   import 将python已有的功能引入脚本直接使用

　　--   argv：参数变量

　　--   解包：script, first, second, third = argv    把argv中的东西解包，将所有的参数一次赋予左边的变量名

　　--   argv 和 raw_input() 有什么不同？

　　　　不同点在于用户输入的时机。如果参数是在用户执行命令时就要输入，那就是 argv，如果是在脚本运行过程中需要用户输入，那就使用 raw_input()。

代码： 

from sys import argv

script, first, second, third = argv

print "The script is called:", script
print "Your first variable is:", first
print "Your second variable is:", second
print "Your third variable is:", third

结果：

习题14：提示与传递

代码：

from sys import argv

script, user_name = argv
prompt = '> '

print "Hi %s, I'm the %s script." % (user_name, script)
print "I'd like to ask you a few questions."
print "Do you like me %s?" % user_name
likes = raw_input(prompt)

print "Where do you live %s?" % user_name
lives = raw_input(prompt)

print "What kind of computer do you have?"
computer = raw_input(prompt)

print '''
　　Alright, so you said %r about liking me.
　　You live in %r. Not sure where that is.
　　And you have a %r computer. Nice.
''' % (likes, lives, computer)

结果：

习题15：读取文件

　　--   涉及两个文件，一个脚本文件.py文件，另一个是ex15_sample.txt

　　第二个文件内容：

This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of fun to have in here.

--   open()  打开文件   返回的是一个“file object”

--   read()  读取文件内容

代码：

from sys import argv

script, filename = argv

txt = open(filename)

print "Here's your file %r:" % filename
print txt.read()

print "Type the filenmae again:"
file_again = raw_input("> ")

txt_again = open(file_again)

print txt_again.read()

结果：

习题16：读写文件

　　--   close  关闭文件

　　--   read  读取文件内容

　　--   readline  读取文本文件中的一行

　　--   write(stuff)   将stuff写入文件

代码：

from sys import argv

script, filename = argv

print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."

raw_input("?")

print "Opening the file..."
target = open(filename, 'w')

print "Truncating the file, Goodbye!"
target.truncate()

print "Now I'm going to ask you for three lines."

line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")

print "I'm going to write these to the file."

target.write(line1)
target.write('\n')
target.write(line2)
target.write('\n')
target.write(line3)
target.write('\n')

print "And finally, we close it."
target.close()

结果：

习题17：更多文件操作

　　--   exists()  判断文件是否存在，存在，继续执行；不存在，新建文件再继续执行

代码：

from sys import argv
from os.path import exists

script, from_file, to_file = argv

print "Copying from %s to %s" % (from_file, to_file)

#we could do these two on one line too, how?
in_file = open(from_file)
indata = in_file.read()

print "The input file is %d bytes long" % len(indata)

print "Does the output file wxist? %r" % exists(to_file)
print "Ready, hit RETURN to continue, CTRL-C to abort."
raw_input()

out_file = open(to_file, 'w')
out_file.write(indata)

print "Alright, all done."

out_file.close()
in_file.close()

结果：

习题18：命名、变量、代码、函数

　　函数可做三洋事情：

　　　1、给代码片段命名，就跟“变量”给字符串和数字命名一样

　　　2、可以接受参数，就跟脚本接受argv一样

　　　3、通过使用#1和#2，可以创建“微型脚本”或者“小命令”

　　介绍：

　　　　def：定义

　　　　函数名：可以随意取，最好能体现出函数的功能来，注意命名规范！不可重复

　　　　参数：放在圆括号内

　　　　格式：def  函数名称  (参数-多个参数以“,”隔开):

　　　　　　　　　函数内容  开始编写前缩进4个空格

　　　　函数可以接收参数，也可以不接收参数

　　　　运行/调用函数，函数名后紧跟(参数-可有可无，可多个)

代码：

# 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'."

print_two("Zed", "Shaw")
print_two_again("Zed", "Shaw")
print_one("First!")
print_none()

结果：

习题19：函数和变量

代码：

def cheese_and_crackers(cheese_count, boxes_of_crackers):
　　print "You have %d cheeses!" % cheese_count
　　print "You have %d boxes of crackers!" % boxes_of_crackers
　　print "Man that's enough for a party!"
　　print "Get a blanket.\n"

print "We can just give the function numbers directry:"
cheese_and_crackers(20, 30)

print "OR, We can use variables from our script:"
amount_of_cheese = 10
amount_of_crackers = 50

cheese_and_crackers(amount_of_cheese, amount_of_crackers)

print "We can even do much inside too:"
cheese_and_crackers(10 + 20, 5 + 6)

print "And we can combine the two, variables and much:"
cheese_and_crackers(amount_of_cheese + 100, amount_of_crackers + 1000)

结果：

习题20：函数和文件

　　--   更多文件操作  seek()   readline()

代码：

from sys import argv

script, input_file = argv

def print_all(f):
　　print f.read()

def rewind(f):
　　f.seek(0)

def print_a_line(line_count, f):
　　print line_count, f.readline()

current_file = open(input_file)

print "First let's print the whole file:\n"

print_all(current_file)

print "Now let's rewind, kind of like a tape."

rewind(current_file)

print "Let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

结果：