CODEWITHSUNDEEP
pythonfile-writing
Bruce Shen
Bruce Shen

Reputation: 11

Read the file while python is still rewriting the file

I am trying to access the content of a file while that file is still being updated. Following is my code that does the writing to file job:

for i in range(100000):
    fp = open("text.txt", "w")
    fp.write(str(i))
    fp.close()
    #time.sleep(1)

My problem now is that whenever I try to open my file while the for loop is still running, I get an empty file in text editor(I except to see an "updated" number). I am wondering is there a way that allows me to view the content of file before the for loop ends?

Thanks in advance for any help: )

Upvotes: 1

Views: 76

Answers (3)

Januka samaranyake
Januka samaranyake

Reputation: 2597

Do not open file inside for loop. It is a bad practice and bad code. Each and every time you create a new object. That is why you get an empty file.

fp = open("text.txt", "r+")
for i in range(100000):
    fp.seek(0)
    fp.write(str(i))
    fp.truncate()
fp.close()

Upvotes: 4

MotKohn
MotKohn

Reputation: 3945

When you write to a file it usually does not actually get written to disk until file is closed. If you want it to be written immediately you need to add a flush to each iteration, hence:

fp = open("text.txt", "w")
for i in range(100000):
    fp.write(str(i))
    fp.write("\n")
    fp.flush()
fp.close()

Upvotes: 0

DYZ
DYZ

Reputation: 57033

Modern operating systems buffer file writes to improve performance: several consecutive writes are lumped together before they are actually written to the disc. If you want the writes to propagate to the disk immediately, use method flush(), but remember that it drastically reduces application performance:

with open("text.txt", "w") as fp:
  for i in range(100000):
    fp.write(str(i))
    fp.flush()

Upvotes: 2

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