python 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
... 
hello davehe
i am emily
emily emily

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()
'hello davehe\n'
>>> f1.readline()
'i am emily\n'
>>> f1.readline()
'emily emily\n'
>>> f1.readline()
''
>>> f1.readline()
''
>>>f1.close()

 FileObject.readlines:返回一个列表

>>> f1 = open("/root/a.txt")
>>> f1.readlines()
['hello davehe\n', 'i am emily\n', 'emily emily\n']''

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()
'hello davehe\n'
>>> f1.next()
'i am emily\n'
>>> f1.next()
'emily emily\n'
>>> f1.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

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()
[email protected]:~# cat a.txt 
hello davehe
i am emily
emily emily
python
python
python

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()
'hello davehe\ni am emily\nemily emily\npython\npython\npython\n'
>>> f1.seek(0,0)     指针指到开头,在读
>>> f1.read()
'hello davehe\ni am emily\nemily emily\npython\npython\npython\n'
>>> f1.read()
''
>>> f1.seek(0,0)
>>> f1.seek(0,2)     指针指到末尾,在读
>>> f1.read()
''

下面看个小实例,查找a.txt中emily出现几次

[email protected]:~# vim file.py 
#!/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()
[email protected]:~# cat a.txt 
hello davehe
i am emily
emily emily
[email protected]:~# python file.py 
this is have 3 emily