Many times students have difficulty understanding reduce() so pay careful attention to this lecture. The function reduce(function, sequence) continually applies the function to the sequence. It then returns a single value.
If seq = [ s1, s2, s3, ... , sn ], calling reduce(function, sequence) works like this:
Lets see an example:
lst =[47,11,42,13] reduce(lambda x,y: x+y,lst)
Lets look at a diagram to get a better understanding of what is going on here:
from IPython.display import Image Image('http://www.python-course.eu/images/reduce_diagram.png')
Note how we keep reducing the sequence until a single final value is obtained. Lets see another example:
#Find the maximum of a sequence (This already exists as max()) max_find = lambda a,b: a if (a > b) else b
#Find max reduce(max_find,lst)
Hopefully you can see how useful reduce can be in various situations. Keep it in mind as you think about your code projects!