Python编程中的文件读写及相关的文件对象方法讲解-Python Tutorial-php.cn

python文件读写

python 进行文件读写的内建函数是open或file

file_hander(文件句柄或者叫做对象)= open(filename,mode)

mode：

模式说明

r 只读

r+ 读写

w 写入,先删除源文件,在重新写入,如果文件没有则创建

w+ 读写,先删除源文件,在重新写入,如果文件没有则创建(可以写入写出)

读文件:

>>> fo = open("/root/a.txt")
>>> fo

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<open file '/root/a.txt', mode 'r' at 0x7f5095dec4e0>

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>>> fo.read()

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'hello davehe\ni am emily\nemily emily\n'

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>>> fo.close()
>>> fo.read()                     #对象已关闭，在读取就读不到

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Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file

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>>> f1 = file("/root/a.txt")         
>>> f1.read()

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'hello davehe\ni am emily\nemily emily\n'

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>>> f1.close()

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写文件:

root@10.1.6.200:~# ls -l new.txt

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ls: cannot access new.txt: No such file or directory

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>>> fnew = open("/root/new.txt",'w')  w参数文件没有则创建
>>> fnew.write('hello \n i am dave')

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这时查看文件数据其实还只是在缓存区中,没有真正落到文件上.

root@10.1.6.200:~# cat new.txt 
root@10.1.6.200:~#

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只要我把文件关闭,数据会从缓存区写到文件里

>>> fnew.close()
root@10.1.6.200:~# cat new.txt

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hello 
i am dave

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再次使用w参数,文件会被清空,所以用该参数需要谨慎.

>>> fnew = open("/root/new.txt","w")

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root@10.1.6.200:~# cat new.txt 
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mode使用r+参数:

>>> fnew = open("/root/new.txt",'r+')
>>> fnew.read()

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'hello dave'

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>>> fnew.write('i am dave')
>>> fnew.close()

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root@10.1.6.200:~# cat new.txt

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hello davei am dave

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这次打开文件,直接写入,会发现ooo替换开头字母,因为上面读取操作使用了指针在写就写在后面.而这次是直接从头写入.

>>> fnew = open("/root/new.txt",'r+')
>>> fnew.write('ooo')
>>> fnew.close()

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root@10.1.6.200:~# cat new.txt

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ooolo davei am dave

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文件对象方法
下面文件对象方法

FileObject.close()
String=FileObject.readline([size])
List = FileObject.readlines([size])
String = FileObject.read([size]) read:读取所有数据
FileObject.next()
FileObject.write(string)
FileObject.writelines(List)
FlieObject.seek(偏移量,选项)
FlieObject.flush() 提交更新

>>> for i in open("/root/a.txt"):  用open可以返回迭代类型的变量,可以逐行读取数据
...   print i
...

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hello davehe
i am emily
emily emily

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FileObject.readline: 每次读取文件的一行,size是指每行每次读取size个字节，直到行的末尾，超出范围会读取空字符串

>>> f1 = open("/root/a.txt")
>>> f1.readline()

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'hello davehe\n'

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>>> f1.readline()

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'i am emily\n'

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>>> f1.readline()

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'emily emily\n'

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>>> f1.readline()
''
>>> f1.readline()
''
>>>f1.close()

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FileObject.readlines:返回一个列表

>>> f1 = open("/root/a.txt")
>>> f1.readlines()

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['hello davehe\n', 'i am emily\n', 'emily emily\n']''

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FileObject.next:返回当前行,并将文件指针到下一行,超出范围会给予警示,停止迭代.

>>> f1 = open("/root/a.txt")
>>> f1.next()

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'hello davehe\n'

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>>> f1.next()

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'i am emily\n'

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>>> f1.next()

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'emily emily\n'

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>>> f1.next()

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Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
StopIteration

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FileObject.write:write和后面writelines在写入前会是否清除文件中原来所有的数据,在重新写入新的内容,取决于打开文件的模式.

FileObject.writelines(List):多行写,效率比write高,速度更快,少量写入可以使用write

>>> l = ["python\n","python\n","python\n"]
>>> f1 = open('/root/a.txt','a')
>>> f1.writelines(l)
>>> f1.close()

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root@10.1.6.200:~# cat a.txt

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hello davehe
i am emily
emily emily
python
python
python

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FlieObject.seek(偏移量,选项):可以在文件中移动文件指针到不同的位置.

位置的默认值为0,代表从文件开头算起(即绝对偏移量),1代表从当前位置算起,2代表从文件末尾算起.

>>> f1 = open('/root/a.txt','r+')
>>> f1.read()

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'hello davehe\ni am emily\nemily emily\npython\npython\npython\n'

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>>> f1.seek(0,0)   指针指到开头,在读
>>> f1.read()

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'hello davehe\ni am emily\nemily emily\npython\npython\npython\n'

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>>> f1.read()
''
>>> f1.seek(0,0)
>>> f1.seek(0,2)   指针指到末尾,在读
>>> f1.read()
''

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下面看个小实例,查找a.txt中emily出现几次

root@10.1.6.200:~# vim file.py

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#!/usr/bin/env python
import re
f1 = open('/root/a.txt')
count = 0
for s in f1.readlines():
  li = re.findall("emily",s)
  if len(li) > 0:
    count = count + len(li)
print "this is have %d emily" % count 
f1.close()

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root@10.1.6.200:~# cat a.txt

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hello davehe
i am emily
emily emily

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root@10.1.6.200:~# python file.py

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this is have 3 emily

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Related labels：

python document Read and write

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