python list comprehension to produce two values in one iteration

Question

I want to generate a list in python as follows -

[1, 1, 2, 4, 3, 9, 4, 16, 5, 25 .....] 

You would have figured out, it is nothing but n, n*n

I tried writing such a list comprehension in python as follows -

lst_gen = [i, i*i for i in range(1, 10)] 

But doing this, gives a syntax error.

What would be a good way to generate the above list via list comprehension?

Answer 1

Use itertools.chain.from_iterable:

>>> from itertools import chain >>> list(chain.from_iterable((i, i**2) for i in xrange(1, 6))) [1, 1, 2, 4, 3, 9, 4, 16, 5, 25] 

Or you can also use a generator function:

>>> def solve(n): ...     for i in xrange(1,n+1): ...         yield i ...         yield i**2  >>> list(solve(5)) [1, 1, 2, 4, 3, 9, 4, 16, 5, 25] 

Answer 2

The question is old, but just for the curious reader, i propose another possibility: As stated on first post, you can easily make a couple (i, i**2) from a list of numbers. Then you want to flatten this couple. So just add the flatten operation in your comprehension.

[x for i in range(1, 10) for x in (i,i**2)]