Simple class for trapping / capturing Python Text IO streams like from subprocess.popen, pexpect, sys.stderr and others; enabling the capture output of or dropping streams with cross platform DEVNULL helper.
python3 -m pip install tiotrap
This tool contains one class TextIOTrap and a helper DEVNULL.
_stdout_bk = sys.stdout # Store original stdout ttrap = tiotrap.TextIOTrap(store=True) try: sys.stdout = ttrap # Map stdout to tiotrap print("TEST1") # call some chatty functions() print("TEST2") finally: sys.stdout = _stdout_bk # Restore stdout
Output of print:
captured logs:
TEST1
<chatty outputs here>
TEST2
aTrap = [] _stdout_bk = sys.stdout try: sys.stdout = tiotrap.TextIOTrap(write_handler=lambda s: aTrap.append(s)) print("TEST1") print("TEST2") finally: sys.stdout = _stdout_bk # print adds extra \n end so remove with rstrip() print(f"aTrap:\n{''.join(aTrap).rstrip()}\n~end~\n")
Output of print:
aTrappedStdout = ['TEST1', 'TEST2']
You can substitute lambda with a function or method call to handle writes with your own code.
ttrap = tiotrap.TextIOTrap(store=True) p = pexpect.spawn('ls -la') p.logfile = ttrap p.expect(pexpect.EOF) print(f"`ls -la` cmd output:\n{ttrap.entries()}\n~")
Output of print:
ls output:
<full directory listing here of cwd>
Other uses of TextIOTrap:
- Output the stdout of a
subprocess.popencall in real time to a secondary log file - ...
ttrap = tiotrap.TextIOTrap(store=True) p = pexpect.spawn('ls -la') p.logfile = ttrap p.expect(pexpect.EOF) print("ls -la` cmd output (as was written):") for write in ttrap: print(write)
Output: Similar to Ex4
_stdout_bk = sys.stdout try: sys.stdout = tiotrap.DEVNULL print("THIS WILL NOT PRINT") finally: sys.stdout = _stdout_bk print("THIS WILL PRINT")
This DEVNULL is very simple implementation and is fully cross platform unlike someother DEVNULL implementations.
Note: TextIOTrap has been set up to be compatible with the standard methods for a Text IO streams. I'll be glad to update if any edge cases are discovered.