Count Specific Values in Dataframe
You could use len([x for x in df["Sex"] if x == "Male"). This iterates through the Sex column of your dataframe and determines whether an element is "Male" or not. If it is, it is appended to a list via list comprehension. The length of that list is the number of Males in your dataframe.
If I had a column in a dataframe, and that column contained two possible categorical variables, how do I count how many times each variable appeared? 
So e.g, how do I count how many of the participants in the study were male or female?
I've tried value_counts, groupby, len etc, but seem to be getting it wrong. 
Thanks