02_solutions.py

# -*- coding: utf-8 -*-
"""02_solutions.py

Author -- Michael Widrich
Contact -- widrich@ml.jku.at
Date -- 01.10.2019

Add tasks 7, 8, 9 by Van Quoc Phuong Huynh -- WS2020

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The following copyright statement applies to all code within this file.

Copyright statement:
This material, no matter whether in printed or electronic form, may be used for
personal and non-commercial educational use only. Any reproduction of this
manuscript, no matter whether as a whole or in parts, no matter whether in
printed or in electronic form, requires explicit prior acceptance of the
authors.

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Example solutions for tasks in file 02_tasks.py.

"""

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# 02 Conditions, for-loops, while-loops, and list comprehensions
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#
# Task 1
#

# Loop through list fnames and count how many elements in the list end with
# '.png'. You can use 'string'.endswith('substring') to check if a string ends
# with a certain substring. Use a for loop to solve this task.
fnames = ['file0.txt', 'file1.png', 'file2.txt', 'file3.txt',
          'file4.png', 'file5.txt', 'file6.txt']

# Your code here #
counter = 0
for fname in fnames:
    if fname.endswith('.png'):
        counter += 1
        
# Alternative solution, since True evaluates to the integer 1:
counter = 0
for fname in fnames:
    counter += fname.endswith('.png')


#
# Task 2
#

# Create a list "some_list" with values from 3 to 100 (100 is excluded). Loop
# through the list some_list and compute the sum of the square root of all
# elements.

# Your code here #
result = 0
for value in range(3, 100):
    result += value ** (1/2)


#
# Task 3
#

# Create a counter "counter" and loop through list "some_list". For each
# element 'not good' add -1, for each element 'okay' add 0, for each element
# 'good' add 1, and for each element 'very good' in the list add 2 to the
# counter.
some_list = ['okay', 'not good', 'okay', 'okay', 'good', 'good', 'okay',
             'very good',  'not good', 'very good']

# Your code here #
counter = 0
for element in some_list:
    if element == 'not good':
        counter += -1
    elif element == 'okay':
        counter += 0
    elif element == 'good':
        counter += 1
    elif element == 'very good':
        counter += 2

# Alternative (ignoring 'okay' since we should add 0):
counter = 0
for element in some_list:
    if element == 'not good':
        counter += -1
    elif element == 'good':
        counter += 1
    elif element == 'very good':
        counter += 2


#
# Task 4
#

# Create a new list from list fnames but add 'image' to the beginning of the
# element if the string ends with '.png' ('file1.png' -> 'imagefile1.png'),
# 'text' if the string ends with '.txt', and 'data' otherwise. You can use
# 'string'.endswith('substring') to check if a string ends with a certain
# substring. Use a for-loop for the task.
fnames = ['file0.txt', 'file1.png', 'file2.txt', 'file3.txt',
          'file4.png', 'file5.txt', 'file6.txt', 'file7.dat']

# Your code here #
new_list = []
for fname in fnames:
    if fname.endswith('.png'):
        new_list.append('image' + fname)
    elif fname.endswith('.txt'):
        new_list.append('text' + fname)
    else:
        new_list.append('data' + fname)


#
# Task 5
#

# Create a new list from list fnames but add 'image' to the beginning of the
# element if the string ends with '.png' ('file1.png' -> 'imagefile1.png'),
# 'text' if the string ends with '.txt', and 'data' otherwise. You can use
# 'string'.endswith('substring') to check if a string ends with a certain
# substring. Use a list-comprehension for the task.
fnames = ['file0.txt', 'file1.png', 'file2.txt', 'file3.txt',
          'file4.png', 'file5.txt', 'file6.txt', 'file7.dat']

# Your code here #
new_list = ['image' + fname if fname.endswith('.png') else
            'text' + fname if fname.endswith('.txt') else
            'data' + fname
            for fname in fnames]


#
# Task 6
#

# Create an empty string 'some_string'. Use the line
user_input = input('Input:\n')
# to get a string as input from the user. Use a while loop to get input
# from the user and append the input to the end of 'some_string'. Escape the
# loop if the user types "end".

# Your code here #
some_string = ''
while True:
    user_input = input('Input:\n')
    some_string += user_input
    if user_input == 'end':
        break

# Better solution (here we first collect the strings in a list and then
# combine them instead of creating a new longer string every iteration):
temp_list = []
while True:
    user_input = input('Input:\n')
    temp_list.append(user_input)
    if user_input == 'end':
        break
some_string = ''.join(temp_list)


#
# Task 7
#

# Merge two sorted lists, list1 and list2, to become a new sorted list
list1 = [1, 4, 7, 8, 12, 30]
list2 = [3, 5, 8, 9, 18, 20, 21, 25]

# Your code here #
len1 = len(list1)
len2 = len(list2)

i = 0
j = 0
merged_list = []

while i < len1 and j < len2:
    e1 = list1[i]
    e2 = list2[j]
    
    if e1 < e2:
        merged_list.append(e1)
        i += 1
    else:
        merged_list.append(e2)
        j += 1

if i == len1:
    merged_list.extend(list2[j:])  # Alternative: merged_list += list2[j:]
else:
    merged_list.extend(list1[i:])


#
# Task 8
#

# Use while ... else ... statement to implement a pseudo-login scenario in
# which a user is asked to enter a password. Use
# password = input("Password: ")
# to get the input of the user as string.
# If the password is correct, print "Login success" and and exit the program.
# Otherwise, let the user try again.
# In case of entering 3 wrong passwords, print
# "Contact the administrator to recover password"
# and exit the program.
# The choice of the correct password is up to you.

# Your code here #
secret_pwd = "secret"
try_count = 0
try_limit = 3

while try_count < try_limit:
    password = input("Password: ")
    if password == secret_pwd:
        print("Login success")
        break
    try_count += 1
else:
    print(f"Contact the administrator to recover password")

#
# Task 9
#

# Given lists of grades of students, make a summarized grade list of students
# following the scheme: <student name>, <grade sum>, <tuple of component grades>
exam1s = [6, 10, 9, 8]
exam2s = [10, 7, 8, 8]
assg1s = [20, 15, 18, 17]
assg2s = [25, 20, 30, 28]
assg3s = [26, 25, 30, 25]
students = ["Alice", "Malice", "Sam", "May"]

# Expected result:
# [['Alice', 87, (6, 10, 20, 25, 26)],
#  ['Malice', 77, (10, 7, 15, 20, 25)],
#  ['Sam', 95, (9, 8, 18, 30, 30)],
#  ['May', 86, (8, 8, 17, 28, 25)]]

# Your code here #
list = [[record[0], record[1] + record[2] + record[3] + record[4] + record[5], record[1:]]
        for record in zip(students, exam1s, exam2s, assg1s, assg2s, assg3s)]
# or
# list = [[record[0], sum(record[1:]), record[1:]] for record in zip(students, exam1s, exam2s, assg1s, assg2s, assg3s)]