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Python Python Collections (2016, retired 2019) Dictionaries Word Count

Posted by Krishna Pratap Chouhan
Krishna Pratap Chouhan
15,203 Points

Python Collections. Return Dictionary out of string.

Why does the following first code passes where as the second code does not.

#PASSES
def word_count(arg):
    var_dict = {}
    arg = arg.lower().split()
    for a in arg:
        if a in var_dict:
            var_dict[a]+=1;
        else:
            var_dict[a] = 1;

    return var_dict

#FAILS
def word_count(arg):
    var_dict = {}
    arg = arg.lower().split(' ')
    #or arg = arg.lower().split(" ")
    for a in arg:
        if a in var_dict:
            var_dict[a]+=1;
        else:
            var_dict[a] = 1;

    return var_dict
wordcount.py 
# E.g. word_count("I do not like it Sam I Am") gets back a dictionary like:
# {'i': 2, 'do': 1, 'it': 1, 'sam': 1, 'like': 1, 'not': 1, 'am': 1}
# Lowercase the string to make it easier.



def word_count(arg):
    var_dict = {}
    arg = arg.lower().split()
    for a in arg:
        if a in dic:
            var_dict[a]+=1;
        else:
            var_dict[a] = 1;

    return var_dict

1 Answer

Travis Howk
Travis Howk
7,169 Points
Travis Howk
Travis Howk
7,169 Points

This is from the python methodology:

If the separator is not specified or is None, [...] runs of consecutive whitespace are regarded as a single separator.

Both executions of your code return identical strings whenever you type in normal stuff. However, they no longer execute the same code whenever you enter a string that consists of only white space. Example:

Using the empty string "", your first algorithm will return an empty dictionary {} as desired. The second algorithm, however, returns {'':1}. Why this occurs can be found here. Basically, it just has to deal with defaults for each of the different algorithms that are launched by the different syntax in each of the respective methods.

Krishna Pratap Chouhan
Krishna Pratap Chouhan
15,203 Points

Thanks Travis that was really helpful. On similar lines:

#str is string with 3 spaces.
str="   "
#len(str) gives me 3
#where as len(str.split(' ')) gives me 4

why is that happening?

Travis Howk
Travis Howk
7,169 Points 
len(str) = 3

This is because there are three spaces. Simple enough

len(str.split(' ')) = 4

This one is a bit more complicated. So whenever you use the split method, the string is going to be split into different bits based on where whatever you told it to split is. So what is happening here is that there aren't any characters in the string other than the spaces, and so you end up with a situation like this:

"   "
"" + " " + "" + " " + "" + " " + ""

Those two above strings are equivalent. The second string shows you what the split function is doing. The reason why it has length 4 is because split(" ") splits the string " " into 4 empty strings as you can count in the above code. You can also see this for yourself if you go print str.split(" "); it will spit out an array that shows you 4 empty strings.

If you find the answers helpful, be sure to upvote them. Let me know if you have any other questions.