Mixing
binary search for list in python
My code for binary search function in a list returns true for a value in the list, but returns None (instead of false) for values not in the list.
Can someone please explain me what I'm doing wrong?
The program is:
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
return("true")
break
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
else:
return("false")
aList=[2,3,5,7,9,12,14,23,34,45,67,89,101]
xnum=int(input("enter a number:"))
searchlist(xnum,aList)
print(searchlist(xnum,aList))
python binary-search
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
add a comment |
My code for binary search function in a list returns true for a value in the list, but returns None (instead of false) for values not in the list.
Can someone please explain me what I'm doing wrong?
The program is:
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
return("true")
break
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
else:
return("false")
aList=[2,3,5,7,9,12,14,23,34,45,67,89,101]
xnum=int(input("enter a number:"))
searchlist(xnum,aList)
print(searchlist(xnum,aList))
python binary-search
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
Without diving into the code,alistis going down to 2 values and it's ending thewhileloop, causing it to returnNone. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like yourelsestatement won't ever execute. Putreturn Falseafter the while loop instead and it should work (I'd suggest useTrueandFalseinstead of strings).
– Peter
Nov 19 '18 at 13:09
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
your secondelifperfomed. If you delete this block, then return('false')
– Rudolf Morkovskyi
Nov 19 '18 at 13:17
add a comment |
My code for binary search function in a list returns true for a value in the list, but returns None (instead of false) for values not in the list.
Can someone please explain me what I'm doing wrong?
The program is:
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
return("true")
break
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
else:
return("false")
aList=[2,3,5,7,9,12,14,23,34,45,67,89,101]
xnum=int(input("enter a number:"))
searchlist(xnum,aList)
print(searchlist(xnum,aList))
python binary-search
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
My code for binary search function in a list returns true for a value in the list, but returns None (instead of false) for values not in the list.
Can someone please explain me what I'm doing wrong?
The program is:
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
return("true")
break
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
else:
return("false")
aList=[2,3,5,7,9,12,14,23,34,45,67,89,101]
xnum=int(input("enter a number:"))
searchlist(xnum,aList)
print(searchlist(xnum,aList))
python binary-search
python binary-search
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
edited Nov 19 '18 at 13:03
mkrieger1
4,30121832
4,30121832
asked Nov 19 '18 at 12:59
nikosL
62
asked Nov 19 '18 at 12:59
nikosL
62
asked Nov 19 '18 at 12:59
nikosL
62
62
Without diving into the code,alistis going down to 2 values and it's ending thewhileloop, causing it to returnNone. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like yourelsestatement won't ever execute. Putreturn Falseafter the while loop instead and it should work (I'd suggest useTrueandFalseinstead of strings).
– Peter
Nov 19 '18 at 13:09
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
your secondelifperfomed. If you delete this block, then return('false')
– Rudolf Morkovskyi
Nov 19 '18 at 13:17
add a comment |
Without diving into the code,alistis going down to 2 values and it's ending thewhileloop, causing it to returnNone. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like yourelsestatement won't ever execute. Putreturn Falseafter the while loop instead and it should work (I'd suggest useTrueandFalseinstead of strings).
– Peter
Nov 19 '18 at 13:09
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
your secondelifperfomed. If you delete this block, then return('false')
– Rudolf Morkovskyi
Nov 19 '18 at 13:17
Without diving into the code,
alist is going down to 2 values and it's ending the while loop, causing it to return None. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like your else statement won't ever execute. Put return False after the while loop instead and it should work (I'd suggest use True and False instead of strings).– Peter
Nov 19 '18 at 13:09
Without diving into the code,
alist is going down to 2 values and it's ending the while loop, causing it to return None. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like your else statement won't ever execute. Put return False after the while loop instead and it should work (I'd suggest use True and False instead of strings).– Peter
Nov 19 '18 at 13:09
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
your second
elif perfomed. If you delete this block, then return ('false')– Rudolf Morkovskyi
Nov 19 '18 at 13:17
your second
elif perfomed. If you delete this block, then return ('false')– Rudolf Morkovskyi
Nov 19 '18 at 13:17
add a comment |
2 Answers
2
active
oldest
votes
You get None when your function does not return a value. This happens because the while loop terminates without going into the "else" branch.
A better practice would be to return True (not the string, but the Boolean value) when you find the value in the list, and return False after the loop.
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
add a comment |
Your while loop cannot catch the else statement. you don't need that else. try this :
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
result = False
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
result = True
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
return result
aList=[2,3,5,7,5,67,89,101]
xnum=int(input("enter a number:"))
print(searchlist(xnum,aList))
answered Nov 19 '18 at 13:33
Ali Kargar
1444
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You get None when your function does not return a value. This happens because the while loop terminates without going into the "else" branch.
A better practice would be to return True (not the string, but the Boolean value) when you find the value in the list, and return False after the loop.
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
add a comment |
You get None when your function does not return a value. This happens because the while loop terminates without going into the "else" branch.
A better practice would be to return True (not the string, but the Boolean value) when you find the value in the list, and return False after the loop.
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
add a comment |
You get None when your function does not return a value. This happens because the while loop terminates without going into the "else" branch.
A better practice would be to return True (not the string, but the Boolean value) when you find the value in the list, and return False after the loop.
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
You get None when your function does not return a value. This happens because the while loop terminates without going into the "else" branch.
A better practice would be to return True (not the string, but the Boolean value) when you find the value in the list, and return False after the loop.
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
answered Nov 19 '18 at 13:14
Yakov Dan
1,258617
1,258617
add a comment |
add a comment |
Your while loop cannot catch the else statement. you don't need that else. try this :
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
result = False
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
result = True
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
return result
aList=[2,3,5,7,5,67,89,101]
xnum=int(input("enter a number:"))
print(searchlist(xnum,aList))
answered Nov 19 '18 at 13:33
Ali Kargar
1444
add a comment |
Your while loop cannot catch the else statement. you don't need that else. try this :
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
result = False
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
result = True
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
return result
aList=[2,3,5,7,5,67,89,101]
xnum=int(input("enter a number:"))
print(searchlist(xnum,aList))
answered Nov 19 '18 at 13:33
Ali Kargar
1444
add a comment |
Your while loop cannot catch the else statement. you don't need that else. try this :
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
result = False
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
result = True
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
return result
aList=[2,3,5,7,5,67,89,101]
xnum=int(input("enter a number:"))
print(searchlist(xnum,aList))
answered Nov 19 '18 at 13:33
Ali Kargar
1444
Your while loop cannot catch the else statement. you don't need that else. try this :
def searchlist(x,alist):
end=int(len(alist)-1)
mid=int(len(alist)/2)
result = False
while len(alist)>2:
if x==alist[mid] or x==alist[0] or x==alist[end] :
result = True
elif x>alist[mid]:
alist=alist[mid:]
mid=int(len(alist)/2)
end=int(len(alist)-1)
elif x<alist[mid]:
alist=alist[:mid]
mid=int(len(alist)/2)
end=int(len(alist)-1)
return result
aList=[2,3,5,7,5,67,89,101]
xnum=int(input("enter a number:"))
print(searchlist(xnum,aList))
answered Nov 19 '18 at 13:33
Ali Kargar
1444
answered Nov 19 '18 at 13:33
Ali Kargar
1444
answered Nov 19 '18 at 13:33
Ali Kargar
1444
answered Nov 19 '18 at 13:33
Ali Kargar
1444
1444
add a comment |
add a comment |
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Without diving into the code,
alistis going down to 2 values and it's ending thewhileloop, causing it to returnNone. I'd suggest print out the current state of the list each loop, and manually run through your code to figure at what point it's not working as expected. Edit: Actually, it looks like yourelsestatement won't ever execute. Putreturn Falseafter the while loop instead and it should work (I'd suggest useTrueandFalseinstead of strings).– Peter
Nov 19 '18 at 13:09
If you want to return false if you don't find what you want in your list you should put the return false after the loop, not in the loop
– Baptiste Gavalda
Nov 19 '18 at 13:12
your second
elifperfomed. If you delete this block, then return('false')– Rudolf Morkovskyi
Nov 19 '18 at 13:17