How to delete multiple defined and undefined variables safely in python?

Question

I am currently using jupyter notebook, and I want to delete variables that are used only within the cell, so that I won't accidentally misuse these variables in other cells.

For example, I want to remove the variable myvar and loop variable i in the following codes:

start = 1
stop = 2
for i in range(start, stop):
    pass
myvar = "A"
# other statements
# ...
del i, myvar # Runs ok, and variables i and myvar are deleted and I won't accidentally use i or myvar in another jupyter notebook cell

This works fine, but there are cases where some variables are actually not defined. In the following example, this throws an error since i is not defined because the loop is never run. The defined variables myvar is not deleted.

start = 1
stop = 1 # Now we have stop equal to 1
for i in range(start, stop):
    pass
myvar = "A"
# other statements
# ...
del i, myvar # NameError, since i is not defined, and myvar is not deleted

I have used contextlib or try-except statements to avoid the error, but still myvar is not deleted.

import contextlib
start = 1
stop = 1
for i in range(start, stop):
    pass
myvar = "A"
# other statements
# ...
with contextlib.suppress(NameError):
    del i, myvar # Error suppressed, but myvar is not deleted

The only work-around is to wrap del statement for every variable I want to delete.

import contextlib
start = 1
stop = 1
for i in range(start, stop):
    pass
myvar = "A"
# other statements
# ...
with contextlib.suppress(NameError): 
    del i
with contextlib.suppress(NameError): 
    del myvar
# ...
# It works but codes get messy if I need to delete many variables

However, this makes codes messy, especially if you have a lot of variables to delete (n lines if there are n variables). Is there any way to delete all defined and undefined variables safely with less messy codes, in one/two lines?

stackoverflow.com/questions/843277/… you can check if variable exist before deleting it — trigonom
– trigonom, Commented Oct 29, 2020 at 15:59
You can check with if 'i' in locals() or use try: del i with except NameError: pass. I'd use the try/except style. But I honestly would not delete variables at all. Define a function for logical units of code, then the variable will be deleted once the function has finished. Or delete your variables at places where they are defined for sure. — Niklas Mertsch
– Niklas Mertsch, Commented Oct 29, 2020 at 16:00

M. Reza Andalibi · Accepted Answer · 2022-05-06 05:43:30Z

13

You can use a comma-separated listing following "del", del var1, var2, var3, to delete selected variables.

answered May 6, 2022 at 5:43

M. Reza Andalibi

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2 Comments

CSStudent7782 Over a year ago

The question references this functionality, and rather than asking if it exists, is asking if there is a way to delete multiple variables whether or not some or all have been defined.

lehiester Mar 27 at 23:16

^ This comment is a good critique in terms of the original question, but this is the top result for some internet searches for the simpler "defined-variable-only" question, and this answer is very effective for that. +1

Kroshka Kartoshka · Accepted Answer · 2020-10-29 16:09:18Z

4

A one-liner to do del x safely:

globals().pop('x', None);

There are many ways to do that, but they need more than 1 line of code, which I guess is not what you look for. Note ; at the end, which prevents the variable from being printed by Jupiter.

edited Oct 29, 2020 at 16:09

answered Oct 29, 2020 at 16:03

Kroshka Kartoshka

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1 Comment

Nic Szerman Over a year ago

this doesn't delete variables from dict

go2nirvana · Accepted Answer · 2020-10-29 15:59:46Z

2

Rather than suppressing errors you could check if variable actually exists by checking if it is in globals() or locals(). You will have to operate string names though and form a del statement to execute it with exec.

to_delete = ['i', 'myvar']
for _var in to_delete:
    if _var in locals() or _var in globals():
        exec(f'del {_var}')

answered Oct 29, 2020 at 15:59

go2nirvana

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