重新梳理Python基础（4）

1. 文件写操作

文件写操作，需要在打开文件的时候添加参数，如

open("filename", "w")

以下是对文件操作的函数小结

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.需要open的时候添加w参数
write(stuff) -- Writes stuff to the file.

参考代码

from sys import argv

script, filename = argv

print "We are going to erase %r." % filename
print "If you don't want that, hit CTRL-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 am 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()

输出

E:\SkyDrive\python\the hard way to learn python>python ex16.py ex16_sample.txt
We are going to erase 'ex16_sample.txt'.
If you don't want that, hit CTRL-C
If you do want that, hit RETURN
?
Opening the file...
Truncating the file. Goodbye!
Now I am going to ask you for three lines.
line 1: I have some books.
line 2: You have some books.
line 3: He has some books.
I'm going to write these to the file.
And finally, we close it.

open模式的小结，参考http://hi.baidu.com/leejun_2005/item/3f6f8ddc8a8b3b56d73aae64

"r"   以读方式打开，只能读文件 ， 如果文件不存在，会发生异常      
"w" 以写方式打开，只能写文件， 如果文件不存在，创建该文件，如果文件已存在，先清空，再打开文件
"rb"   以二进制读方式打开，只能读文件 ， 如果文件不存在，会发生异常      
"wb" 以二进制写方式打开，只能写文件， 如果文件不存在，创建该文件，如果文件已存在，先清空，再打开文件
"rt"   以文本读方式打开，只能读文件 ， 如果文件不存在，会发生异常      
"wt" 以文本写方式打开，只能写文件， 如果文件不存在，创建该文件，如果文件已存在，先清空，再打开文件
"rb+"   以二进制读方式打开，可以读、写文件 ， 如果文件不存在，会发生异常      
"wb+" 以二进制写方式打开，可以读、写文件， 如果文件不存在，创建该文件，如果文件已存在，先清空，再打开文件

　　

2. 把一个文件写到另一个文件

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)

in_file = open(from_file)
fromdata = in_file.read()

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

print "Does the output file exist? %r" % exists(to_file) #如果不存在，会新建这个文件
print "Ready, hit RETURN to continue, CTRL-C to abort."
raw_input()
out_file = open(to_file, "w")
out_file.write(fromdata)

print "All done"

out_file.close()
in_file.close()

3. 贴个无聊的代码吧

from sys import argv
from os.path import exists

script, input_file = argv

print "Is %r exsit?" % input_file
exists(input_file)
indata = """I have a book.
You have two.
He has three.
"""
open(input_file, "w").write(indata)


def print_all(f):
    print f.read()

def rewind(f):
    f.seek(0)

def print_a_line(line_count, f):
    print str(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 tap."

rewind(current_file)

print "Let's print three lines"

current_line = 1
print_a_line(current_line, current_file)

# current_line = current_line + 1
current_line += 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)