`print()` in a loop doesn't output until the loop is done #825

jean · 2020-07-17T05:35:47Z

I paste some code into the BPython REPL.
It looks like nothing happened, I don't even see the code I pasted, but it is running.

When I interrupt the loop, all this appears at once:

>>> import time
>>> 
>>> # seen_nodes = []
>>> # dupe_nodes = []
>>> counter = 0
>>> for row in col.get_rows():
...     node_id = row.get_property('node_id') 
...     if (node_id in seen_nodes) and (node_id not in dupe_nodes):
...         dupe_nodes.append(node_id)
...     elif node_id not in seen_nodes:
...         seen_nodes.append(node_id)
...     counter += 1
...     if not counter % 2:
...         print(f'{counter:6} | seen: {len(seen_nodes)}, dupes: {len(dupe_nodes)}', flush=True)
...         time.sleep(1)
... 
     2 | seen: 12530, dupes: 100
     4 | seen: 12530, dupes: 102
     6 | seen: 12530, dupes: 104
     8 | seen: 12530, dupes: 106
Traceback (most recent call last):
  File "<input>", line 10, in <module>
    time.sleep(1)
  File "/home/jean/.local/lib/python3.8/site-packages/bpython/curtsiesfrontend/coderunner.py", line 176, in sigint_handler
    raise KeyboardInterrupt()
KeyboardInterrupt

etiennerichart · 2020-07-23T01:14:35Z

Hey Jean, I can't reproduce this. Maybe it's something else in the rest of your code. Could you share it with us? Also, what version of bpython are you using?

thomasballinger · 2020-07-23T02:09:03Z

Oh I missed a critical detail here, this is only when you paste the code in.

Here's a smaller repro: copy this code and paste it into bpython.

import time
for i in range(10):
    print(i)
    time.sleep(.1)

print('done')

bpython / bpython

`print()` in a loop doesn't output until the loop is done #825

`print()` in a loop doesn't output until the loop is done #825

jean commented Jul 17, 2020

etiennerichart commented Jul 23, 2020

thomasballinger commented Jul 23, 2020 •

edited

bpython / bpython

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`print()` in a loop doesn't output until the loop is done #825

`print()` in a loop doesn't output until the loop is done #825

Comments

jean commented Jul 17, 2020

etiennerichart commented Jul 23, 2020

thomasballinger commented Jul 23, 2020 • edited

thomasballinger commented Jul 23, 2020 •

edited