"""
This module shows how to ITERATE (i.e. loop) through a SEQUENCE
in ways OTHER than just going thru the sequence from BEGINNING to END.
It also shows how to SELECT items in a sequence, e.g.:
-- the items that are strings
-- the items that are even integers (e.g. 2, 4, 6, ...)
Note that:
-- SELECTING items that ARE even integers
is different from:
-- LOOKING only at items AT even-numbered indices.
Authors: David Mutchler, Vibha Alangar, Dave Fisher, Matt Boutell, Mark Hays,
Mohammed Noureddine, Sana Ebrahimi, Sriram Mohan, their colleagues and
PUT_YOUR_NAME_HERE.
""" # TODO: 1. PUT YOUR NAME IN THE ABOVE LINE.
###############################################################################
# TODO: 2. READ the program below and RUN it.
# ___
# When you have read it, asking questions as needed,
# and you feel that you understand:
# -- how to loop through a sequence
# in ways OTHER than just from BEGINNING to END,
# -- how to SELECT items in sequence
# -- the distinction between:
# -- SELECTING items that ARE even integers and
# -- LOOKING only at items AT even-numbered indices.
# then:
# change the above _TODO_ to DONE.
###############################################################################
def main():
""" Calls the TEST functions in this module. """
run_test_sum_string_lengths()
run_test_sum_even_integers()
run_test_sum_items_at_even_indices()
###############################################################################
# The TEST functions are further down in the file,
# so that you can focus on the following examples.
###############################################################################
def sum_string_lengths(sequence, m, n):
"""
What comes in:
-- A sequence of strings
-- Integers m and n,
where 0 <= m <= n < length of the sequence
(which ensures that you can safely use m and n as indices)
What goes out:
Returns the sum of the lengths of the strings
at indices m to n, inclusive, with the restriction
that the loop must go thru the sequence BACKWARDS.
Side effects: None.
Examples:
Suppose that sequence is:
["five", "OK", "songs", "roxanne", "the police", "", "three"]
Then:
-- sum_string_lengths(sequence, 1, 3)
returns the length of "roxanne"
plus the length of "songs" plus the length of "OK",
which is 7 + 5 + 2, which is 14.
-- sum_string_lengths(sequence, 2, 6)
returns the length of "three"
plus the length of "" plus the length of "the police"
plus the length of "roxanne" plus the length of "songs,
which is 5 + 0 + 10 + 7 + 5, which is 27.
Type hints:
:type sequence: list or tuple (of strings)
:type m: int
:type n: int
"""
# -------------------------------------------------------------------------
# EXAMPLE 1. Iterates through PART of a sequence, BACKWARDS.
# -------------------------------------------------------------------------
total = 0
for k in range(n, m - 1, -1):
s = sequence[k]
total = total + len(s)
return total
# Here is an alternative (there are other alternatives as well):
total = 0
for k in range(m, n + 1):
total = total + len(sequence[m + n - k])
return total
def sum_even_integers(sequence):
"""
What comes in:
-- A sequence
What goes out:
Returns the sum of the items in the sequence that:
-- are integers AND
-- are even.
Side effects: None.
Examples:
sum_even_integers([3, 10, 6, 5, 5, 10])
returns 10 + 6 + 10, which is 26
sum_even_integers([3, 9, 10, 99, 101, 5, 6, 5, 5, 10])
still returns 10 + 6 + 10, which is 26
sum_even_integers(["hello", 3, 10, 6, "bye", 5, 7.33, 5, 10])
still returns 10 + 6 + 10, which is 26
Type hints:
:type sequence: list or tuple
"""
# -------------------------------------------------------------------------
# EXAMPLE 2. Iterates through a sequence,
# identifying and summing the items that are EVEN INTEGERS.
#
# Note how:
# -- The TYPE function returns the TYPE of its argument.
# -- An integer X is EVEN if the remainder is 0
# when you divide X by 2 and take the remainder.
# -------------------------------------------------------------------------
total = 0
for k in range(len(sequence)):
item = sequence[k]
if type(item) is int:
if item % 2 == 0:
total = total + item
return total
# Here is an alternative (there are other alternatives as well):
total = 0
for k in range(len(sequence)):
if (type(sequence[k]) is int) and (sequence[k] % 2 == 0):
total = total + sequence[k]
return total
def sum_items_at_even_indices(sequence):
"""
What comes in:
-- A sequence of numbers.
What goes out:
Returns the sum of the numbers in the list that:
-- are at EVEN INDICES.
Side effects: None.
Examples:
sum_items_at_even_indices([3, 10, 6, 5, 5, 10])
returns 3 + 6 + 5, which is 14
sum_items_at_even_indices([5.5, 10, 3, 2, 10, 0, 1])
returns 5.5 + 3 + 10 + 1, which is 19.5
Type hints:
:type sequence: list or tuple (of numbers)
"""
# -------------------------------------------------------------------------
# EXAMPLE 3. Iterates through and sums the items in a list
# of numbers that are at even INDICES.
#
# Constrast this example with the previous example.
# -------------------------------------------------------------------------
total = 0
for k in range(0, len(sequence), 2):
total = total + sequence[k]
return total
# Here is a ** BAD alternative ** that computes the right result
# but takes twice as long to do so as needed.
total = 0
for k in range(len(sequence)): # This is a BAD solution
if k % 2 == 0:
total = total + sequence[k]
return total
###############################################################################
# Just TEST functions below here.
###############################################################################
def run_test_sum_string_lengths():
""" Tests the sum_string_lengths function. """
print()
print("--------------------------------------------------")
print("Testing the sum_string_lengths function:")
print("--------------------------------------------------")
seq = ["five", "OK", "songs", "roxanne", "the police", "", "three"]
total1 = sum_string_lengths(seq, 1, 3)
total2 = sum_string_lengths(seq, 2, 6)
print("Returned, expected:", total1, 14)
print("Returned, expected:", total2, 27)
def run_test_sum_even_integers():
""" Tests the sum_even_integers function. """
print()
print("--------------------------------------------------")
print("Testing the sum_even_integers function:")
print("--------------------------------------------------")
total1 = sum_even_integers([3, 10, 6, 5, 5, 10])
total2 = sum_even_integers(["hello", 3, 10, 6, "bye", 5, 7.33, 5, 10])
total3 = sum_even_integers([3, 9, 10, 99, 101, 5, 6, 5, 5, 10])
print("Returned, expected:", total1, 26)
print("Returned, expected:", total2, 26)
print("Returned, expected:", total3, 26)
def run_test_sum_items_at_even_indices():
""" Tests the sum_items_at_even_indices function. """
print()
print("--------------------------------------------------")
print("Testing the sum_items_at_even_indices function:")
print("--------------------------------------------------")
total1 = sum_items_at_even_indices([3, 10, 6, 5, 5, 10])
total2 = sum_items_at_even_indices([5.5, 10, 3, 2, 10, 0, 1])
print("Returned, expected:", total1, 14)
print("Returned, expected:", total2, 19.5)
# -----------------------------------------------------------------------------
# Calls main to start the ball rolling.
# -----------------------------------------------------------------------------
main()