Dictionaries
"""
Dictionaries are a mapping of keys to values. This module shows how to
access, modify, remove and extend key-value pairs with this data
structure.
"""
# Module-level constants
_GPA_MIN = 0.0
_GPA_MAX = 4.0
def main():
# Let's create a dictionary with student keys and GPA values
student_gpa = {"john": 3.5, "jane": _GPA_MAX, "bob": 2.8, "mary": 3.2}
# There are four student records in this dictionary
assert len(student_gpa) == 4
# Each student has a name key and a GPA value
assert len(student_gpa.keys()) == len(student_gpa.values())
# We can get the names in isolation. Note that in Python 3.7 and
# above, dictionary entries are sorted in the order that they were
# defined or inserted
student_names = []
for student in student_gpa.keys():
student_names.append(student)
assert student_names == ["john", "jane", "bob", "mary"]
# We can check that `student_gpa` has the names that were stored
# in `student_names` from the loop above
for student in student_names:
assert student in student_gpa
# We can get the GPAs in isolation
gpa_values = []
for gpa in student_gpa.values():
gpa_values.append(gpa)
assert gpa_values == [3.5, _GPA_MAX, 2.8, 3.2]
# We can get the GPA for a specific student
assert student_gpa["john"] == 3.5
# We can update the GPA for a specific student
student_gpa["john"] = _GPA_MAX
# Or update the GPA for multiple students
student_gpa.update(bob=_GPA_MIN, mary=_GPA_MIN)
# We can access the student and GPA simultaneously
gpa_binary = []
for student, gpa in student_gpa.items():
assert student_gpa[student] == gpa
gpa_binary.append(gpa)
assert gpa_binary == [_GPA_MAX, _GPA_MAX, _GPA_MIN, _GPA_MIN]
# Let's remove all the students
for student in student_names:
student_gpa.pop(student)
assert len(student_gpa) == 0
# Let's add all the students back in
for student, gpa in zip(student_names, gpa_binary):
student_gpa[student] = gpa
assert len(student_gpa) == len(student_names)
if __name__ == "__main__":
main()
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