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  1. """Test readahead buffer in pipes [1]
  2.  
  3. [1]:  http://b...content-available-to-author-only...n.org/issue3907
  4.  
  5. - `for line in p.stdout` fails on Python 2
  6. - `for line in iter(p.stdout.readline, b'')` succeeds on Python 2
  7. - both work on Python 3
  8. """
  9. import sys
  10. import time
  11. from subprocess import Popen, PIPE
  12.  
  13. def test_proc(use_iter=False, timeout=1):
  14.     p = Popen([sys.executable, "-c", """import sys, time
  15. for i in range(2):
  16.     print(i)
  17.     sys.stdout.flush()
  18.     time.sleep(%d)
  19.     """ % timeout], stdout=PIPE, bufsize=1)
  20.  
  21.     if use_iter:
  22.         it = iter(p.stdout.readline, b'')
  23.     else:
  24.         it = p.stdout
  25.  
  26.     elapsed = []
  27.     start = time.time()
  28.     for line in it:
  29.         elapsed.append(time.time() - start)
  30.         print("%s %.2f" % (line.decode().rstrip(), elapsed[-1]))
  31.     assert min(elapsed) < timeout
  32.     assert max(elapsed) < 2*timeout
  33.  
  34. test_proc(use_iter=True)
  35. test_proc(use_iter=False)
  36.  
Runtime error #stdin #stdout 0.25s 9344KB
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stdin
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Standard input is empty
stdout
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0 0.08
1 1.08
0 2.09
1 2.09
https://ideone.com/8KFawl
language:
Python (cpython 2.7.16)
created:
10 years ago
visibility:
secret

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