Python编程中的文件读写及相关的文件对象方法讲解

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

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

> fo.read()

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

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

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

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

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

> f1.close()

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

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

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

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

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

hello 
i am dave

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

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

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

'hello dave'

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

root@10.1.6.200:~# cat new.txt 

hello davei am dave

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

root@10.1.6.200:~# cat new.txt 

ooolo davei am dave

> 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

> 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()

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

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

> 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

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

root@10.1.6.200:~# cat a.txt 

hello davehe
i am emily
emily emily
python
python
python

> 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()
''

root@10.1.6.200:~# 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()

root@10.1.6.200:~# cat a.txt 

hello davehe
i am emily
emily emily

root@10.1.6.200:~# python file.py 

this is have 3 emily