Blog
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Redirecting stderr in Python: Using contextlib.redirect_stderr
Want stderr in your Python program to go somewhere else? Use redirect_stderr in contextlib:
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redirect_stdout in Python: Sending print output to a file
Writing a bunch to non-stdout in Python? You might want to use redirect_stdout from contextlib:
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Python stderr: Printing with sys.stderr and the file kwarg
Want to print to stderr, not stdout, in a Python program? Use sys.stderr and the “file” kwarg: stdout and stderr often look identical in a terminal — but they aren’t!
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Python print to a file: Using the file keyword argument
Normally, “print” in Python writes to stdout. Write elsewhere with the “file” keyword argument:
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Redirecting sys.stdout: Assigning print output to a file
Want stdout from your Python program to go elsewhere? Assign sys.stdout to a writeable file. (Don’t forget to keep the original around!) Better: print’s file kwarg.
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Python frozen modules: Why they have no __file__ attribute
After you import a Python module, its repr (printed representation) shows its name and the loaded file. But some modules don’t have files; they were “frozen” into Python. They have no __file__ attribute, and show “frozen” in their __loader__.
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importlib.reload: Reimporting a Python module during development
Once you import a Python module, a second import won’t reload it. That’s usually good. But what if you want to? (Common in development and debugging.) This forces the reload.
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Python import: How a module name becomes a file on sys.path
You import a Python module with the variable you’ll define, not a filename. “import mymod” tells Python to find mymod.py in each dir in sys.path. The first directory is ” (the empty string) — i.e., the directory where the program is running (i.e., not where it was defined).
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PYTHONPATH: A scalable alternative to sys.path.insert
Want Python to import modules in non-default dirs? You could do this: But: It doesn’t scale across many programs. And what if the dir changes? Better: Set the PYTHONPATH environment variable — scalable and set in one place.
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sys.path supports zipfiles: Importing modules from an archive
sys.path tells Python where to look when importing a module. Think of it as a list of directories. But it also handles zipfiles. A zipfile in sys.path is treated as a directory. Files in the zipfile can be imported.