如何使用python itertools模块

Question

I have got the following code:

import itertools


x = ['Lebron' 'James']
y = ['is', 'the', 'goat']
z = ['is', 'not', 'the', 'goat']
itertools.chain(x, y)

And I get the following output: itertools.chain at 0x104baab50

What does this output mean? And how can I see the result of the method?

Then the same for the code below:

itertools.chain.from_iterable([x,y])

I get the following output: itertools.chain at 0x104af7550

What does this mean? And how can I see the actual result of the method? I'm not quite sure what the difference is between the two methods.

Answer 1

itertools.chain returns a iterator that will allow you to iterate through the values in a for loop, via __next__ , etc. like a regular Python iterator .

For example:

In [3]: import itertools
   ...: x = ['Lebron', 'James']
   ...: y = ['is', 'the', 'goat']
   ...: z = ['is', 'not', 'the', 'goat']

In [4]: for thing in x:
   ...:     print('Thing is', thing)
   ...:
Thing is Lebron
Thing is James

In [5]: for thing in itertools.chain(x, y):
   ...:     print('Thing is', thing)
   ...:
Thing is Lebron
Thing is James
Thing is is
Thing is the
Thing is goat

and from_iterable takes and iterable (eg a list) of iterables (eg other lists) and iterates over each in turn:

In [8]: for thing in itertools.chain.from_iterable([x, y]):
   ...:     print('Thing is', thing)
   ...:
Thing is Lebron
Thing is James
Thing is is
Thing is the
Thing is goat

Answer 2

Simply put, chain is not a function; it's a type . Like most types, you get back an instance of that type when you call it. The instance chain(x,y) is iterable; it first yields elements from x , and when it exhausts x , it yields elements from y .

chain.from_iterable is a class method; it's definition is effectively the same as

def from_iterable(itr):
    return chain(*itr)

assuming you could use * with an arbitrary iterable.

Answer 3

You should see more about the itertools module in Python Docs .

What does this output mean? And how can I see the result of the method?

An itertools.chain object was returned. This is a generator. You can see the result in such a way for example (iterate through the values using for loop):

for item in itertools.chain(x, y):
   print(item)

or this way (make a list from this iterable):

print(list(itertools.chain(x, y)))

itertools.chain(*iterables)

Here you are passing several iterables to create a chain from as a function arguments directly:

itertools.chain(x, y)

itertools.chain.from_iterable(iterable)

And here you are passing a single iterable which contains other iterables to create a chain from:

itertools.chain.from_iterable([x, y])