Python：即使列表中的项目存在，如果列表中的项目仍为False

Question

I was trying to solve this Question in HackerRank.

#t=int(input().strip())
t=1
for i in range(0,t):
    #u=input()
    #pw=str(input()).split(' ')
    #s=input().strip()
    u=6
    pw=['because', 'can','do', 'must', 'we', 'what']
    s="wedowhatwemustbecausewecan"
    pw_in_s=[]
    for p in pw:
        if p in s:        
            pw_in_s.append(p)
    print(pw_in_s)
    start=0
    length=1
    res=""
    while start+length<=len(s):
        tmp=s[start:start+length]
        print (tmp)
        if tmp in pw_in_s:
            res+=" "+tmp
            start=length
            length=1            
        else:
            length=length+1   
    print(res)

The code is not complete to solve the question. But I'm stuck in halfway.

Problem

Even though the list pw_in_s contains an item 'do' , the if tmp in pw_in_s is not getting satisfied when tmp is 'do' . Also the program runs into an infinite loop, because length value is not getting incremented.

Where is the problem?

Answer 1

Even though the list pw_in_s contains an item 'do' the if tmp in pw_in_s is not getting satisfied when tmp is 'do'.

I can't reproduce that problem.

Also the program is in an infinite loop.

That happens in the code path for if tmp in pw_in_s: which doesn't necessarily make progress toward the termination condition on each iteration. Setting start=length and length=1 doesn't get you closer to making start+length bigger than len(s) .

For debugging, change print (tmp) to print(start, length, len(s), tmp, pw_in_s, (tmp in pw_in_s)) .