Python Challenge level 3 – Solving with string slicing

apologies to posting the question, as has been answered in other questions as well. However, couldn’t figure out what’s wrong with this solution. The question requires to find the lower-cased characters bordered by 3 upper-cased characters on each side. The code i’ve writting:

q = ''
for i in range(4,len(x)-4):
    if x[i].islower() and x[i-4].islower() and x[i+4].islower() and x[i-3:i].isupper() and x[i+1:i+4].isupper()  :
        q+=x[i]


print(q)

The string i’m getting is

‘lgvcaaginbkvsoezhtlnldslyitlooqfgiksudtm’ vs ‘linkedlist’

Thanks for the help.

Edit: for some reason the following code seems to work:

q = ''
for i in range(4,len(x)-4):
    if x[i].islower() and x[i-4].islower() and  x[i-3:i].isupper() and x[i+1:i+4].isupper() and x[i+4].islower():
        q+=x[i]

print(q)

Answer

What you are trying to do is match a pattern : Not Upper, Upper, Upper, Upper, Not Upper, Upper, Upper, Upper, Not Upper. This is easier to catch if you use a signature for your string:

>>> t = "This is some TEXtTHAt will result in one true result"
>>> sig = "".join("U" if c.isupper() else "l" for c in t)
>>> sig
'UllllllllllllUUUlUUUllllllllllllllllllllllllllllllll'

You are looking for the lUUUlUUUl substrings in the sig string. Python has no builtin for findall, but you can to iterate over the results of find:

>>> result = ""
>>> i = sig.find("lUUUlUUUl")
>>> while i != -1: # find != -1 means that the substring wasn't found
...     result += t[i+4] # the center `l` 
...     i = sig.find("lUUUlUUUl", i+4) # we can start the next search at the center `l`
... 
>>> print( result )
t

You may also use re.finditer with a regex pattern, but is more complicated.