The result of inline and usual for loops are different-CodePudding

I have a tree which I want to return its children as a list through a function. In the function, I needed to iterate over a list of strings. At first I did it by using the inline foor loop

    def get_children(root):
        
        Data = [ ]
        Data.append( root.data )
        
        for child in root.children:
              Data.append( elem for elem in get_children(child) )
        return Data

however, I got the following strange result

['Electronics', <generator object get_children.<locals>.<genexpr> at 0x7fb3a081a3c0>, <generator object get_children.<locals>.<genexpr> at 0x7fb3a081a7b0>, <generator object get_children.<locals>.<genexpr> at 0x7fb3a081a9e0>]

Then, I changed the inline for loop into a typical one and the problem is resolved, i.e.,

   for elem in get_children(child):
        Data.append( elem )

I was wondering if you help me to understand why this happened. I've read a similar post about list comprehension, however, I still have confusion to understand the difference here.

CodePudding user response：

Because you didn't wrap your list comprehension with [], the return value of it is a generator expression (which generates the list you made). You can fix this by simply wrapping the expression with []

CodePudding user response：

you used Generator expressions instead of list comprehension Generator Expressions are somewhat similar to list comprehensions, but the former doesn’t construct list object. Instead of creating a list and keeping the whole sequence in the memory the generator generates the next element in demand.

CodePudding user response：

The problem is here at Data.append( elem for elem in get_children(child)), you haven't wrapped the list comprehension. So the solution is Data.append([elem for elem in get_children(child)]) to just add [ at start and ] at end of list comprehension.

I think yo are trying to get all child of the root, well here's solution from Getting every child widget of a Tkinter window

root.winfo_children()

You can use this instead of for-loop, as this would provide you with every children of root window.