I got an err “IOError: [Errno 0] Error” with this python program:
from sys import argv
file = open("test.txt", "a+")
print file.tell() # not at the EOF place, why?
print file.read() # 1
file.write("Some stuff will be written to this file.") # 2
# there r some errs when both 1 & 2
print file.tell()
file.close()
what seems to be the problem? These 2 cases below are ok:
from sys import argv
file = open("test.txt", "a+")
print file.tell() # not at the EOF place, why?
# print file.read() # 1
file.write("Some stuff will be written to this file.") # 2
# there r some errs when both 1 & 2
print file.tell()
file.close()
and:
from sys import argv
file = open("test.txt", "a+")
print file.tell() # not at the EOF place, why?
print file.read() # 1
# file.write("Some stuff will be written to this file.") # 2
# there r some errs when both 1 & 2
print file.tell()
file.close()
still, why
print file.tell() # not at the EOF place, why?
does not print the size of the file, is “a+” the append-mode? then the file pointer should point to EOF?
i’m using Windows 7 and Python 2.7.
Answers:
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Method 1
Python uses stdio’s fopen function and passes the mode as argument. I am assuming you use windows, since @Lev says the code works fine on Linux.
The following is from the fopen documentation of windows, this may be a clue to solving your problem:
When the “r+”, “w+”, or “a+” access type is specified, both reading
and writing are allowed (the file is said to be open for “update”).
However, when you switch between reading and writing, there must be an
intervening fflush, fsetpos, fseek, or rewind operation. The current
position can be specified for the fsetpos or fseek operation, if
desired.
So, the solution is to add file.seek() before the file.write() call. For appending to the end of the file, use file.seek(0, 2).
For your reference, file.seek works as follows:
To change the file object’s position, use f.seek(offset, from_what).
The position is computed from adding offset to a reference point; the
reference point is selected by the from_what argument. A from_what
value of 0 measures from the beginning of the file, 1 uses the current
file position, and 2 uses the end of the file as the reference point.
from_what can be omitted and defaults to 0, using the beginning of the
file as the reference point.
[reference: http://docs.python.org/tutorial/inputoutput.html]
As mentioned by @lvc in the comments and @Burkhan in his answer, you can use the newer open function from the io module. However, I want to point out that the write function does not work exactly the same in this case — you need to provide unicode strings as input [Simply prefix a u to the string in your case]:
from io import open
fil = open('text.txt', 'a+')
fil.write('abc') # This fails
fil.write(u'abc') # This works
Finally, please avoid using the name ‘file’ as a variable name, since it refers to a builtin type and will be silently over-written, leading to some hard to spot errors.
Method 2
The solution is to use open from io
D:>python
Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> f = open('file.txt','a+')
>>> f.tell()
0L
>>> f.close()
>>> from io import open
>>> f = open('file.txt','a+')
>>> f.tell()
22L
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0