In a lot of notebooks when folks want to release unused dataframes and other objects from memory I see two slightly different lines:
\ngc.collect()_ = gc.collect()Just wondering why/when you'd use one.
\nSuper-Grandmaster @cdeotte uses both at different times in the below notebook…
\nhttps://www.kaggle.com/code/cdeotte/xgboost-starter-0-793
The code gc.collect() works every time. The reason I use _ = gc.collect() sometimes is to prevent gc from printing text to output when it is the last line in a code cell.
In general, using the underscore in Python _ is a common practice to ignore output of a function. So for example, if a function returns two things like
def example_function()\n return 5, 10\nAnd we write x,_ = example_function(), then the variable x receives the first output 5 and the _ is a convention for ignoring the output 10.
thanks for the super fast reply!
\nDo you ever take a day off :)
", "rawMarkdown": "thanks for the super fast reply!\n\nDo you ever take a day off :)", "votes": 4 }, { "id": 1864401, "postDate": "2022-07-21T03:36:14.393Z", "content": "Hehe, I found out the reason when I removed all of the second version from my copy of the notebook 😆
", "rawMarkdown": "Hehe, I found out the reason when I removed all of the second version from my copy of the notebook 😆", "votes": 1 }, { "id": 1864626, "postDate": "2022-07-21T07:50:16.770Z", "content": "The explanation from @cdeotte about the underscore is incorrect.
\n\n\nusing the underscore in Python _ is a way to send the output of a function to Python garbage collection.
\n
_ is a normal Python variable name. It has nothing to do with garbage collection whatsoever.
From the documentation:
\n\n\n[..] _ is a regular identifier. It is often used to name “special” items, but it is not special to Python itself.
\n
as you can see:
\n>>> for x, _ in enumerate(range(2,0,-1)):\n... print(x, _)\n0 2\n1 1\nSo _ = gc.collect() assigns the return value of gc.collect() to the variable _ (preventing a notebook to print it, if in last line, as mentioned above).
Sorry for the nitpicking, but I find those things important.
", "rawMarkdown": "The explanation from @cdeotte about the underscore is incorrect.\n\n> using the underscore in Python _ is a way to send the output of a function to Python garbage collection.\n\n`_` is a normal Python variable name. It has nothing to do with garbage collection whatsoever.\n\nFrom [the documentation](https://docs.python.org/3/reference/lexical_analysis.html#reserved-classes-of-identifiers):\n\n> [..] _ is a regular identifier. It is often used to name “special” items, but it is not special to Python itself.\n\nas you can see:\n\n```\n>>> for x, _ in enumerate(range(2,0,-1)):\n... print(x, _)\n0 2\n1 1\n```\n\nSo `_ = gc.collect()` assigns the return value of `gc.collect()` to the variable `_` (preventing a notebook to print it, if in last line, as mentioned above).\n\nSorry for the nitpicking, but I find those things important.", "votes": 2 }, { "id": 1865474, "postDate": "2022-07-21T20:42:36.020Z", "content": "Thanks for the clarification @arigion . I updated my post above for correctness.
\nFYI, the symbol _ is special in Python. After any command, we can use _ to access the result of the previous command. For example
>>> 1 + 2\n3\n>>> _\n3\n>>> 3 + 4\n7\n>>> _\n7\n>>> _ + 2\n9\nBut if we assign a value to _ then it behaves like a normal variable like you say. So
>>> 1 + 2\n3\n>>> _\n3\n>>> _ = 9\n>>> 3 + 4\n7\n>>> _\n9\nThat's strange. (I thought after assignment, it would get overwritten with any new command but it does not). So after using it, then it becomes a variable and it will no longer show the last command unless we explicitly delete the variable with del _. Then it returns to being a special character.
In a lot of notebooks when folks want to release unused dataframes and other objects from memory I see two slightly different lines:
\ngc.collect()_ = gc.collect()Just wondering why/when you'd use one.
\nSuper-Grandmaster @cdeotte uses both at different times in the below notebook…
\nhttps://www.kaggle.com/code/cdeotte/xgboost-starter-0-793
The code gc.collect() works every time. The reason I use _ = gc.collect() sometimes is to prevent gc from printing text to output when it is the last line in a code cell.
In general, using the underscore in Python _ is a common practice to ignore output of a function. So for example, if a function returns two things like
def example_function()\n return 5, 10\nAnd we write x,_ = example_function(), then the variable x receives the first output 5 and the _ is a convention for ignoring the output 10.
thanks for the super fast reply!
\nDo you ever take a day off :)
", "votes": 4, "replies": [] }, { "id": 1864401, "author_name": "Robert Hatch", "author_url": "", "post_date": "2022-07-21T03:36:14.393000", "content": "Hehe, I found out the reason when I removed all of the second version from my copy of the notebook 😆
", "votes": 1, "replies": [] }, { "id": 1864626, "author_name": "Arigion", "author_url": "", "post_date": "2022-07-21T07:50:16.770000", "content": "The explanation from @cdeotte about the underscore is incorrect.
\n\n\nusing the underscore in Python _ is a way to send the output of a function to Python garbage collection.
\n
_ is a normal Python variable name. It has nothing to do with garbage collection whatsoever.
From the documentation:
\n\n\n[..] _ is a regular identifier. It is often used to name “special” items, but it is not special to Python itself.
\n
as you can see:
\n>>> for x, _ in enumerate(range(2,0,-1)):\n... print(x, _)\n0 2\n1 1\nSo _ = gc.collect() assigns the return value of gc.collect() to the variable _ (preventing a notebook to print it, if in last line, as mentioned above).
Sorry for the nitpicking, but I find those things important.
", "votes": 2, "replies": [] }, { "id": 1865474, "author_name": "Chris Deotte", "author_url": "", "post_date": "2022-07-21T20:42:36.020000", "content": "Thanks for the clarification @arigion . I updated my post above for correctness.
\nFYI, the symbol _ is special in Python. After any command, we can use _ to access the result of the previous command. For example
>>> 1 + 2\n3\n>>> _\n3\n>>> 3 + 4\n7\n>>> _\n7\n>>> _ + 2\n9\nBut if we assign a value to _ then it behaves like a normal variable like you say. So
>>> 1 + 2\n3\n>>> _\n3\n>>> _ = 9\n>>> 3 + 4\n7\n>>> _\n9\nThat's strange. (I thought after assignment, it would get overwritten with any new command but it does not). So after using it, then it becomes a variable and it will no longer show the last command unless we explicitly delete the variable with del _. Then it returns to being a special character.