How to find out where is the file pointer
Find out the position of a file pointer
seek(offset[, whence]) moves the file pointer to the position described by offset and whence.
offset is a byte (character) count. whence defaults to 0, which means that the offset is
from the beginning of the file.
whence may also be set to 1 (move relative to current position:
the offset may be negative), or 2 (move relative
to the end of the file).
f = open(r'c:\text\somefile.txt', 'w')
f.write('01234567890123456789')
f.seek(5) # ww w. ja v a2 s . c om
f.write('Hello, World!')
f.close()
f = open(r'c:\text\somefile.txt')
print f.read()
Move around within the file using seek().
f = open('/tmp/x', 'w+')
print f.tell()# from ww w .j a va 2 s .c o m
f.write('test line 1\n') # add 12-char string [0-11]
print f.tell()
print f.write('test line 2\n') # add 12-char string [12-23]
print f.tell() # tell us current file location (end))
print f.seek(-12, 1) # move back 12 bytes
print f.tell() # to beginning of line 2
print f.readline()
print f.seek(0, 0) # move back to beginning
print f.readline()
print f.tell() # back to line 2 again
print f.readline()
print f.tell() # at the end again
print f.close() # close file
Use tell() function to find out file position
tell() method returns the current file position.
f = open(r'c:\text\somefile.txt', 'w')
f.write('01234567890123456789')
f.seek(5)# ww w. jav a 2 s.c o m
f.write('Hello, World!')
f.close()
f = open(r'c:\text\somefile.txt')
print f.read()
f = open(r'c:\text\somefile.txt')
print f.read(3)
print f.read(2)
print f.tell()
Handling I/O Errors
The following code shows how to safely open and read from a file and gracefully handle errors.
try:
fsock = open(filename, "rb", 0)
try: # from w ww.j a v a 2 s.c om
fsock.seek(-128, 2)
tagdata = fsock.read(128)
finally:
fsock.close()
except IOError:
pass