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Python Python Collections (2016, retired 2019) Sets Set Math

Sohail Mirza
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.a{fill-rule:evenodd;}techdegree
Sohail Mirza
Python Web Development Techdegree Student 5,158 Points

explanation of how the code works

I have got this code from a previous student. I am trying to reverse engineer it but finding it difficult. Could someone please break this down for how this works from line 3 downwards

sets.py
COURSES = {
    "Python Basics": {"Python", "functions", "variables",
                      "booleans", "integers", "floats",
                      "arrays", "strings", "exceptions",
                      "conditions", "input", "loops"},
    "Java Basics": {"Java", "strings", "variables",
                    "input", "exceptions", "integers",
                    "booleans", "loops"},
    "PHP Basics": {"PHP", "variables", "conditions",
                   "integers", "floats", "strings",
                   "booleans", "HTML"},
    "Ruby Basics": {"Ruby", "strings", "floats",
                    "integers", "conditions",
                    "functions", "input"}
}
def covers(x):
    courses_list = []
    for course in COURSES:
        if x.intersection(COURSES[course]):
            courses_list.append(course)
    return courses_list

1 Answer

Steven Parker
Steven Parker
215,939 Points

Here's a breakdown:

  courses_list = []                     # start with an empty list
  for course in COURSES:                # check each course, one at a time
    if x.intersection(COURSES[course]): # if the set (x) has anything in common with the course 
      courses_list.append(course)       # then add the name of the course to the list
  return courses_list                   # finally return the new list  

Note that an intersection is only those items both sets have in common. If it is empty, it will be "falsey" to the "if". But if there is at least one thing in it, it will be "truthy".

Does that clear it up?