I've been learning about generators in Python recently and have a question. I've used iterators before when learning Java, so I know how they basically work.
So I understand what's going on here in this question: Python for loop and iterator behavior
Essentially, once the for loop traverses through the iterator, it stops there, so doing another for loop would continue the iterator at the end of it (and result in nothing being printed out). That is clear to me
I'm also aware of the tee method from itertools, which lets me "duplicate" a generator. I found this to be helpful when I want to check if a generator is empty before doing anything to it (as I can check whether the duplicate in list form is empty).
In a code I'm writing, I need to create many of the same generators at different instances throughout the code, so my line of thought was: why don't I write a method that makes a generator? So every time I need a new one, I can call that method. Maybe my misunderstanding has to do with this "generator creation" process but that seemed right to me.
Here is the code I'm using. When I first call the method and duplicate it using tee, everything works fine, but then once I call it again after looping through it, the method returns an empty generator. Does this "using a method" workaround not work?
node_list=[]
generate_hash_2, temp= tee(generate_nodes(...))
for node in list(temp):
node_list.append(...)
print("Generate_hash_2:{}".format(node_list))
for node in generate_hash_2:
if node.hash_value==x:
print x
node_list2=[]
generate_hash_3, temp2= tee(generate_nodes(...)) #exact same parameters as before
for node in list(temp2):
node_list2.append(...)
print("Generate_hash_3:{}".format(node_list2))
`
def generate_nodes(nodes, type):
for node in nodes:
if isinstanceof(node.type,type):
yield node
Please ignore the poor variable name choices but the temp2 prints out fine, but temp3 prints out an empty list, despite the methods taking identical parameters :( Note that the inside of the for loop doesn't modify any of the items or anything. Any help or explanation would be great!
For a sample XML file, I have this:
<top></top>
For a sample output, I'm getting:
Generate_hash_2:["XPath:/*[name()='top'][1], Node Type:UnknownNode, Tag:top, Text:"]
Generate_hash_3:[]
If you are interested in helping me understand this further, I've been writing these methods to get an understanding of the files in here: https://github.com/mmoosstt/XmlXdiff/tree/master/lib/diffx , specifically the differ.py file
The code in that file constantly calls the _gen_dx_nodes() method (with the same parameters), which is a method that creates a generator. But the code's generator never "ends" and forces the writer to do something to reset it. So I'm confused why this happens to me (because I've been running into my problem when calling that method from different methods in succession). I've also been using the same test cases so I'm pretty lost here on how to fix this. Any help would be great!
