October 10, 2020 | 6:29am

By force of habit, Ryan Lewis is still living out of his suitcase.

Playing for eight NFL teams in four seasons with stints lasting as short as two weeks offers a lesson, but Lewis can earn the right to unpack Sunday if he is able to stabilize a major weakness for the Giants. He likely will be the third different starter in five games at No. 2 cornerback — tested early and often by the Cowboys’ top-ranked passing attack.

“Being a defensive back in the NFL is no walk in the park,” Lewis told The Post. “One wrong step left or right, and you could get beat. You have to have a short memory. You can’t stop until the game is over. You can give up a couple deep balls and have the game-winning pick at the end. It’s all about your being your biggest fan and staying in it.”

Cut by Washington on Sept. 5, Lewis joined the Giants’ practice squad on Sept. 8, was elevated to the active roster Sept. 19, debuted Sept. 27 and took more than 42 snaps for benched starter Isaac Yiadom last Sunday.

The rapid ascension is the intersection of team need and familiarity because Lewis first learned a variant of this defense with the Patriots in 2017 and then played under Giants coordinator Patrick Graham when the two were with the Dolphins last season.

Ryan Lewis
Ryan LewisN.Y. Post: Charles Wenzelberg

“I’ve always seen myself as a man-to-man corner,” Lewis said. “I feel comfortable pressing [receivers]. They keep the schemes real simple here so guys can learn quickly and execute. I’ve studied this defense inside-out for three years now, and it will allow me to just go out there and just play and not think too much.”

Lewis is the son of former Seahawks and Chiefs scouting executive Will Lewis, the nephew of former Giants defensive coordinator Tim Lewis (2004-06) and the cousin of “Monday Night Football” analyst Louis Riddick — the runner-up to be Giants general manager in 2018. That’s a lot of NFL knowledge in one family.

“My dad was [Riddick’s] mentor and Louis has taken on a little bit of that same role for me,” Lewis said. “He’s very insightful on things to do in the league and how you can separate yourself from the competition. But I’ve always been a sponge toward my dad. I even did a business-class project on how he does his job. It’s something I definitely want to do when I’m done playing.”

First things first: The Cowboys are averaging 407.8 passing yards per game and have three game-breaking receivers in Amari Cooper, CeeDee Lamb and Michael Gallup. Dak Prescott has a 100.5 passer rating in eight career games against the Giants.

It’s a lot to ask of even an experienced cornerback.

“RyLew has been a hard worker since he got here,” safety Jabrill Peppers said. “He knows the nature of this league, and he honed in on his technique and fundamentals. We saw it in practice, so I’m happy that, when he got his number called, he performed.”

Giants defensive backs coach Jerome Henderson says it would be ideal to settle on one cornerback (rather than a rotation) playing opposite James Bradberry. The ship appears to have sailed for season-opening starter Corey Ballentine.

“Ryan showed a lot of positive things in terms of how he played on outside routes,” coach Joe Judge said. “We have to keep putting him in positions where he can really use his speed and some of his instincts to make plays for us.”

Lewis’ instincts should tell him to keep doing whatever he’s doing right now.

“I’ve gotten real comfortable living out of my suitcase, and my girlfriend doesn’t like that,” he joked. “It’s been a different type of career, but I’m living out my dream. If this is how it is, then looking back it’s going to be a crazy story.

“As soon as I got here, my focus was on helping the team win. I’ve been staying at home, grinding, watching film. Maybe when the season is over, I’ll unpack that suitcase.”