I have built a zip object and by accident I noticed that if I apply list() to this object twice, second time it will yield []. My code is shown below:
coordinate = ['x', 'y', 'z']
values = [5, 7, 9]
my_map = zip(coordinate, values)
my_map_list_first = list(my_map)
my_map_list_second = list(my_map)
print(my_map_list_first)
print(my_map_list_second)
Output of the code is:
[('x', 5), ('y', 7), ('z', 9)]
[]
I am new to Python so my terminology may not be 100% accurate. I have tried finding the explanation online, but problem here is what is the actual question. (Good question makes half he answer). Since I am still learning Python, I probably don't know what to ask.
I also tried using that Python simulator which I saw in another topic: http://www.pythontutor.com/visualize.html#mode=display But I only saw what I knew - that my_map_list_second is [], not what exactly is going on under the hood. Can someone explain what happened here? And also point me in a right direction regarding "similar" issues, although I am sure those will become clear in time, as I progress with Python.
This is also my first port on these forums. Thanks in advance.
You are looking for awnser about generator.
In fact, zip will create a generator, that is not process until you iterate trought it, using list in your exemple. An other important property is that generator can only be iterate once.
The last property explain why you get en empty list the second time.