Clear variable in python

Question

Is there a way to clear the value of a variable in python?

For example if I was implementing a binary tree:

class Node:
    self.left = somenode1
    self.right = somenode2

If I wanted to remove some node from the tree, I would need to set self.left to empty.

Asked By: Bnicholas

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Source

Answer 1

What’s wrong with self.left = None?

Answered By: bnaul

Answer 2

The del keyword would do.

>>> a=1
>>> a
1
>>> del a
>>> a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined

But in this case I vote for self.left = None

Answered By: starrify

Answer 3

var = None “clears the value”, setting the value of the variable to “null” like value of “None”, however the pointer to the variable remains.

del var removes the definition for the variable totally.

In case you want to use the variable later, e.g. set a new value for it, i.e. retain the variable, None would be better.

Answered By: user11788

Answer 4

Actually, that does not delete the variable/property. All it will do is set its value to None, therefore the variable will still take up space in memory. If you want to completely wipe all existence of the variable from memory, you can just type:

del self.left

Answered By: Viraj Shah

Answer 5

If want to totally delete it use del:
```
del your_variable
```
Or otherwise, to make the value None:
```
your_variable = None
```
If it’s a mutable iterable (lists, sets, dictionaries, etc, but not tuples because they’re immutable), you can make it empty like:
```
your_variable.clear()
```

Then your_variable will be empty

Answered By: U12-Forward

Answer 6

Do you want to delete a variable, don’t you?

ok, I think I’ve got a best alternative idea to @bnaul’s answer:

You can delete individual names with del:

del x

or you can remove them from the globals() object:

for name in dir():
    if not name.startswith('_'):
        del globals()[name]

This is just an example loop; it defensively only deletes names that do not start with an underscore, making a (not unreasoned) assumption that you only used names without an underscore at the start in your interpreter. You could use a hard-coded list of names to keep instead (whitelisting) if you really wanted to be thorough. There is no built-in function to do the clearing for you, other than just exit and restart the interpreter.

Modules you’ve imported (like import os) are going to remain imported because they are referenced by sys.modules; subsequent imports will reuse the already imported module object. You just won’t have a reference to them in your current global namespace.

Answered By: Federico Migueletto

Answer 7

Delete its contents by setting it to None and then del to remove its pointer from memory

variable = None; del variable

Answered By: Umair Ayub

Clear variable in python

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