What the last output of liftover means?

Question

[ManuelDB]

from pyliftover import LiftOver

lo = LiftOver('hg17', 'hg18')

lo.convert_coordinate('chr1', 1000000)

[('chr1', 949796, '+', 21057807908)]

What '+' and 21057807908 mean?

[Wayne]

The doc string for the function spells out what it returns.

Answer 1

[supertech]

This is the comment from author's script posted on github.

  Note that coordinates are 0-based, and even at negative strand are relative to the beginning of the genome.
    I.e. position 0 strand + is the first position of the genome. Position 0 strand - is also the first position of the genome 
    (and the last position of reverse-complemented genome).

Answer 2

[Pierre Lindenbaum]

https://github.com/konstantint/pyliftover/blob/master/pyliftover/liftover.py#L66

Returns a list of possible conversions for a given chromosome position. The list may be empty (no conversion), have a single element (unique conversion), or several elements (position mapped to several chains). The list contains tuples (target_chromosome, target_position, target_strand, conversion_chain_score), where conversion_chain_score is the "alignment score" field specified at the chain used to perform conversion. If there are several possible conversions, they are sorted by decreasing conversion_chain_score.