fix: do not use mutable objects for function argument defaults

[n1lanjan]

This PR fixes usage of mutable defaults in a some methods. The usage of mutable defaults does not have any adverse impact currently since the object initial_session is not updated in the methods as of now, but any change in the future may introduce bugs due to this and hence a good practice not to use mutable defaults and instead initialise the mutable object inside the function body.

Why It’s Dangerous

• Unintended Persistence: Changes to the default argument persist between calls, violating the expectation of a "fresh" default.
• Subtle Bugs: The behaviour is counterintuitive and can lead to hard-to-debug issues.
• Scope Risks: Even if unused, mutable defaults risk accidental mutation in complex functions.

For eg.

def f(a, L=[]):
    L.append(a)
    return L

print(f(1))
print(f(2))
print(f(3))

will print

[1]
[1, 2]
[1, 2, 3]

To further see why it is bad, please see

• mutable-argument-default (B006)
• Python documentation: Default Argument Values

[hangfei]

Thanks for spotting this! I think this is already fixed recently. Please contribute more to this repo in the future!