CODEWITHSUNDEEP
pythonfile
Ohad
Ohad

Reputation: 143

Writing into a file then reading it on Python 3.6.2

target=open("test.txt",'w+')
target.write('ffff')
print(target.read())

When running the following python script (test.txt is an empty file), it prints an empty string.

However, when reopening the file, it can read it just fine:

target=open("test.txt",'w+')
target.write('ffff')
target=open("test.txt",'r')
print(target.read())

This prints out 'ffff' as needed.

Why is this happening? Is 'target' still recognized as having no content, even though I updated it in line 2, and I have to reassign test.txt to it?

Upvotes: 3

Views: 1573

Answers (3)

omu_negru
omu_negru

Reputation: 4770

Try flushing, then seeking the beginning of the file:

f = open(path, 'w+')
f.write('foo')
f.write('bar')
f.flush()
f.seek(0)
print(f.read())

Upvotes: 1

Martijn Pieters
Martijn Pieters

Reputation: 1121884

A file has a read/write position. Writing to the file puts that position at the end of the written text; reading starts from the same position.

Put that position back to the start with the seek method:

with open("test.txt",'w+') as target:
    target.write('ffff')
    target.seek(0)  # to the start again
    print(target.read())

Demo:

>>> with open("test.txt",'w+') as target:
...     target.write('ffff')
...     target.seek(0)  # to the start again
...     print(target.read())
...
4
0
ffff

The numbers are the return values of target.write() and target.seek(); they are the number of characters written, and the new position.

Upvotes: 10

Richard Neumann
Richard Neumann

Reputation: 3361

No need to close and re-open it. You just need to seek back to the file's starting point before reading it:

with open("test.txt",'w+') as f:
    f.write('ffff')
    f.seek(0)
    print(f.read())

Upvotes: 4

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