How to Fix Minimum Window Substring Errors

def minw(s,t):
    need=Counter(t); have=0
    need_len=len(need); res=''
    l=0
    for r,c in enumerate(s):
        if c in need:
            need[c]-=1
            if need[c]==0: have+=1
        while have==need_len:
            if not res or r-l+1<len(res): res=s[l:r+1]
            if s[l] in need:
                if need[s[l]]==0: have-=1
                need[s[l]]+=1
            l+=1
    return res

from collections import Counter
def minw(s,t):
    need=Counter(t); have=0; need_len=len(need)
    l=0; res=(0,float('inf'))
    for r,c in enumerate(s):
        if c in need:
            need[c]-=1
            if need[c]==0: have+=1
        while have==need_len:
            if r-l+1<res[1]-res[0]+1: res=(l,r)
            if s[l] in need:
                if need[s[l]]==0: have-=1
                need[s[l]]+=1
            l+=1
    return s[res[0]:res[1]+1] if res[1]!=float('inf') else ''