double if condition in a Python for loop

Question

I am working on a python exercise that asks:

# Return True if the string "cat" and "dog" appear the same number of
# times in the given string. 
# cat_dog('catdog') → True
# cat_dog('catcat') → False
# cat_dog('1cat1cadodog') → True

This is my current code:

def cat_dog(str):
   c=0
   d=0
   for i in range(len(str)-2):
     if str[i:i+3]=="cat":
       c=+1
     if str[i:i+3]=="dog":
       d=+1
   return (c-d)==0.0

I look at it and I think it should work but it failed some of the tests, which suggest to me I am not understanding something in how Python logic works. Any explanation as to why my solution is not working would be great. These are all the test results:

cat_dog('catdog') → True            True          OK        
cat_dog('catcat') → False           False         OK        
cat_dog('1cat1cadodog') → True      True          OK        
cat_dog('catxxdogxxxdog') → False   True          X     
cat_dog('catxdogxdogxcat') → True   True          OK            
cat_dog('catxdogxdogxca') → False   True          X  
cat_dog('dogdogcat') → False        True          X
cat_dog('dogdogcat') → False        True          OK        
cat_dog('dog') → False              False         OK        
cat_dog('cat') → False              False         OK        
cat_dog('ca') → True                True          OK        
cat_dog('c') → True                 True          OK        
cat_dog('') → True                  True          OK

I think you mean c += 1 and d += 1 instead of c=+1 and d=+1 — dazedconfused
– dazedconfused, Commented Jan 15, 2015 at 3:28

John La Rooy · Accepted Answer · 2015-01-15 03:28:24Z

6

You should have

c += 1 instead of c = +1

and

d += 1 instead of d = +1

answered Jan 15, 2015 at 3:28

John La Rooy

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Comments

Óscar López · Accepted Answer · 2015-01-15 03:28:04Z

5

A simpler way to solve this problem would be to use built-in string functions, like this:

def cat_dog(s):
    return s.count('cat') == s.count('dog')

answered Jan 15, 2015 at 3:28

Óscar López

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2 Comments

ryanpattison Over a year ago

how is the code making the assumption that they appear next to one another?

MyCarta Over a year ago

I was going to ask the same

score 3 · Accepted Answer · 2015-01-15 03:45:12Z

3

Here is a one-liner for your program;

cat_dog=lambda str1: str1.count("cat")==str1.count("dog")
print (cat_dog("catcat"))

It will return True if counts are equal, else returning False. But if this confused you, here long one.

def cat_dog(str1):
    c="cat"
    d="dog"
    a=str1.count(c)
    b=str1.count(d)
    if a==b:
        return True
    return False
print (cat_dog('catcat'))

Here is a better method. count is very usefull for your program. Less codes, because readability counts.

print (cat_dog('catcat')) -False
print (cat_dog('catdog')) -True

edited Jan 15, 2015 at 3:45

answered Jan 15, 2015 at 3:27

user4447887

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