This is what it would appear at first glance without knowing that female snakes are the heterogamete. While the ball python has not had its genome sequenced, other species of snakes have had their genome sequenced and they have followed this rule. Obviously we cannot know for certain if the ball python follows this as well without sequencing its genome, but the possibility that it differs is unlikely.
If it turned out that the male was the heterogamete it would solve this problem. But as ohhwataloser stated, burms and balls have been hybridized, making it even more unlikely.
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