Questions #1

def foo (bar = []):
bar append( 1 )
return bar
foo()
>>> [ 1 ]
foo()
[ 1 , 1 ]
foo()
>>> [ 1 , 1 , 1 ]

It is considered good practice to specify an empty immutable value for the parameter, for example 0, None, '', False. In the body of the function, check for fullness and create a new collection:

def foo (bar = None ):
if bar is None :
bar = []
bar append( 1 )
return bar
foo()
>>> [ 1 ]
foo()
>>> [ 1 ]
foo()
>>> [ 1 ]

The above is relevant incl. for sets and dictionaries.

Is it possible to pass a function as an argument to another function?
It is possible, a function in Python is a first-order object: it allows assignment, transfer to a function, deletion.
Is it possible to declare a function inside another function? Where will she be seen?
Can. Such a function will only be visible inside the first function.
What are lambdas? What are their features?
These are anonymous functions. They do not reserve a name in a namespace. Lambdas are often passed to map, reduce, filter functions.
Lambdas in Python can only consist of one expression. Using the parenthesis syntax, you can wrap the body of a lambda into multiple lines.
You cannot use a semicolon to separate statements.
Are the following expressions allowed?

• 
  nope=lambda:pass
  
• 
  riser = lambda x: raise Exception(x)
  

No, loading the module will throw a SyntaxError exception. The body of a lambda can only contain an expression. pass and raise are statements.

Decorators

What are decorators? Why are they needed?
Decorator in a broad sense is a design pattern when one object changes the behavior of another. In Python, a decorator is usually a function A that takes a function B and returns a function C. In this case, the C function uses the B function in itself.
To decorate a function means to replace it with the result of the decorator.