problems using pythom tempfile module

[samir.vds]

Hello everyone,

I'm trying to test the tempfile module with the following script,
which basically creates a temporary file, fills the file with some
test data and prints it.

import tempfile

t = tempfile.TemporaryFile()
t.write("lalalala")
t.flush()
print t.read()

Unfortunately, the print statement gives me an empty string. Can
somebody tell me what I'm doing wrong ?


regards Samir

 

[buffi]

Hello everyone,

I'm trying to test the tempfile module with the following script,
which basically creates a temporary file, fills the file with some
test data and prints it.

import tempfile

t = tempfile.TemporaryFile()
t.write("lalalala")
t.flush()
print t.read()

Unfortunately, the print statement gives me an empty string. Can
somebody tell me what I'm doing wrong ?

regards Samir

Do a t.seek(0) before you do the read to "rewind" the file and then it
should work.

 

[samir.vds]

Do a t.seek(0) before you do the read to "rewind" the file and then it
should work.

Ok, this really worked. Can you elaborate why I have to insert this
statement?

 

[Steve Holden]

Ok, this really worked. Can you elaborate why I have to insert this
statement?

Each file has a "current position". As you write a file the current
position moves to stay just ahead of what's been written. So if you read
it without resetting the current position (back to the beginning with
seek(0)) you will get an immediate end of file (i.e. 0 bytes) returned.

regards
Steve
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[buffi]

Pretend that you have a number that is always pointing somewhere in
your temporary file.
It starts a 0.
If you then write "lalalala" (8 characters) it will point after these
at position 8, so that you can write more stuff after your previous
text later by calling write.

The read method reads all the data from the current position of the
"pointer" to the end of the file. If you simply call it after writing,
you wont get anything since you are already at the end of the file.
Therefore you "rewind" the pointer back to the start by calling seek
which takes the position in the file to go to...
your_file.seek(0) returns you to the start of the file to read all of
its data

- Björn Kempén