CODEWITHSUNDEEP
python-3.xpipestdin
frans
frans

Reputation: 9758

In Python how do I read data from stdin until piped process terminates?

I'd like to do something like this:

data = json.load(open(sys.argv[1]) if len(sys.argv) > 1 else sys.stdin)

which for this example can be reduced to 

data = json.load(sys.stdin)

But json.load runs a single .read() which might not contain the whole JSON string I provided via

generate_json_output | myprogram.py

Is there a recommended way to read from stdin until generate_json_output terminates? I tried to catch BrokenPipeError but it doesn't get raised when I run

while True:
    data += sys.stdin.read()

Upvotes: 1

Views: 743

Answers (1)

Abhinav Goyal
Abhinav Goyal

Reputation: 1455

Instead of a while loop, you can use for loop like below to iterate over stdin.

import sys

data = ''
for line in sys.stdin:
    data += line

which can be written as one expression:

data = "".join(sys.stdin)

Running this with input generated using a pipe reads the stdin until it terminates.

t.json:

{
    'a': 2,
    'b': 3
}

Running cat t.json | python a.py prints the complete file to stdout.

Upvotes: 1

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