How to realize it in lambda function?

Question

Examples:
s=say_my_name -> sayMyName
s1=all-you-need-is-love -> allYouNeedIsLove
s2=The_truth_is_out_there -> TheTruthIsOutThere
s3=hello -> hello

#My attempts:

#res = lambda s: ''.join([j[i+1] for i in range(len(s)-1) for j in s if j[i] == '_' or j[i]])

res = lambda s: ''.join([s[i+1].upper() for i in range(len(s)-1) if s[i] == '_' or s[i]])

print(res('say_no_more'))

#why it doesn't work?can someone help, thanks:)

######another way######
I've solve it this way, but i need the lambda:

import re
p = [s[match.start()]+s[match.end()] for match in re.finditer('_', s)]
# p >>> ['_m', '_n']

for c in p:
if c in s:
s = s.replace(c,c[1].upper())

print(s)

Answer 1

"The_truth_is_out_there" -> "TheTruthIsOutThere"

For this one case, first word isn't converted to lowercase? shouldn't it be "theTruthIsOutThere"?

https://code.sololearn.com/c95qNRd1h6aT/?ref=app

Answer 2

Almost good, but not:
res = lambda s: ''.join([s[i+1].upper() if s[i] in ['_', '-'] else s[i] for i in range(len(s)) ])