FIRST PUBLISHED HERE WITH SOME DETAILED EXPLANATIONS

link to all the questions

link to the markdown file

1. Find all numbers divisible by 7 but not a multiple of 5, between 2000 and 3200 (both sides included).

The numbers obtained should be printed in a comma-separated sequence on a single line.

# 1. most intuitive way
for number in range(2000,3201):
        if (number%7 == 0) and (number%5 != 0):
            print(number,end = ",")
 

2002,2009,2016,2023,2037,2044,2051,2058,2072,2079,2086,2093,2107,2114,2121,2128,2142,2149,2156,2163,2177,2184,2191,2198,2212,2219,2226,2233,2247,2254,2261,2268,2282,2289,2296,2303,2317,2324,2331,2338,2352,2359,2366,2373,2387,2394,2401,2408,2422,2429,2436,2443,2457,2464,2471,2478,2492,2499,2506,2513,2527,2534,2541,2548,2562,2569,2576,2583,2597,2604,2611,2618,2632,2639,2646,2653,2667,2674,2681,2688,2702,2709,2716,2723,2737,2744,2751,2758,2772,2779,2786,2793,2807,2814,2821,2828,2842,2849,2856,2863,2877,2884,2891,2898,2912,2919,2926,2933,2947,2954,2961,2968,2982,2989,2996,3003,3017,3024,3031,3038,3052,3059,3066,3073,3087,3094,3101,3108,3122,3129,3136,3143,3157,3164,3171,3178,3192,3199,
 

# 2. use list and join
l=[]
for i in range(2000, 3201):
    if (i%7==0) and (i%5!=0):
        # str() very important coz join only work on strings
        l.append(str(i))
','.join(l)

'2002,2009,2016,2023,2037,2044,2051,2058,2072,2079,2086,2093,2107,2114,2121,2128,2142,2149,2156,2163,2177,2184,2191,2198,2212,2219,2226,2233,2247,2254,2261,2268,2282,2289,2296,2303,2317,2324,2331,2338,2352,2359,2366,2373,2387,2394,2401,2408,2422,2429,2436,2443,2457,2464,2471,2478,2492,2499,2506,2513,2527,2534,2541,2548,2562,2569,2576,2583,2597,2604,2611,2618,2632,2639,2646,2653,2667,2674,2681,2688,2702,2709,2716,2723,2737,2744,2751,2758,2772,2779,2786,2793,2807,2814,2821,2828,2842,2849,2856,2863,2877,2884,2891,2898,2912,2919,2926,2933,2947,2954,2961,2968,2982,2989,2996,3003,3017,3024,3031,3038,3052,3059,3066,3073,3087,3094,3101,3108,3122,3129,3136,3143,3157,3164,3171,3178,3192,3199'
 

# 3. one liner 
# see here for a very common caveat
# https://stackoverflow.com/questions/60379194/why-join-doesnt-work-on-a-list-comprehension
','.join([str(number) for number in range(2000,3201) if number%7 == 0 and number%5 != 0])

# 4. use filter see https://www.geeksforgeeks.org/filter-in-python/
numbers = range(2000,3201)
result = filter(lambda x: x%7 == 0 and x%5 !=0, numbers)
print(list(result)

2. Compute the factorial of a given numbers.

Suppose the following input is supplied to the program:

8

Then, the output should be:

40320

def factorial(number):
  # prevent some user input bug
  if number < 0:
    raise ValueError("No negative numbers please")
    # this is called the base case in recursion
  elif number == 0:
    return 1
  return number*factorial(number-1)
factorial(0)

1

for some nice introduction to recursion, see https://www.khanacademy.org/computing/computer-science/algorithms/recursive-algorithms/a/recursive-factorial

When we're computing n! in this way, we call the first case, where we immediately know the answer, the base case, and we call the second case, where we have to compute the same function but on a different value, the recursive case.

3. Compute power and use dictionary

With a given integral number n, write a program to generate a dictionary that contains (i, i*i) such that is an integral number between 1 and n (both included). and then the program should print the dictionary.

Suppose the following input is supplied to the program:

8

Then, the output should be:

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64}

def powerNumber(number):
    output = {} # or dict() if takes user input use int(input("please enter a number"))
    for i in range(1,number):
      output[i] = i*i
    return output
print(powerNumber(3))

{1: 1, 2: 4}

​

4. Convert comma separated string

Write a program which accepts a sequence of comma-separated numbers from console and generate a list and a tuple which contains every number

input: 34,67,55,33,12,98

output:

[‘34’, ‘67’, ‘55’, ‘33’, ‘12’, ‘98’]

(‘34’, ‘67’, ‘55’, ‘33’, ‘12’, ‘98’)

L = "34,67,55,33,12,98".split(",") # the join syntax is with ".",join(L)
print(L)
print(tuple(L))

['34', '67', '55', '33', '12', '98']
('34', '67', '55', '33', '12', '98')

5. Class and methods

getString: to get a string from console input.
printString: to print the string in upper case.
Also please include simple test function to test the class methods.

## the self parameter is a must, but not the others, see the setString method for a comparaison
class upper:
    def __init__(self):
        self.text = ""
    def getString(self):
#         self.text = "test"
        self.text = input("please type a string here")
    def upper(self):
        print(self.text.upper())
    def setString(self,newText):
        self.text = newText
# No new keyword, class is kind of like a function in Python
test = upper()
test.getString()
test.upper()

please type a string herehehe
HEHE

For more about class see https://www.geeksforgeeks.org/python-classes-and-objects/
​
raw_input() does not exist in Python 3.x, while input() does. Actually, the old raw_input() has been renamed to input()

6. Formula

Q = Square root of [(2 * C * D)/H]

C is 50. H is 30.

D is the variable whose values should be input to your program in a comma-separated sequence.

Input: 100,150,180

Output: 18,22,24

import math
c=50
h=30
value = []
# items = input("please enter comma separated numbers").split(',')
items = "100,150,180".split(',')
for d in items:
    # note the use of float() and str()
    value.append(str(int(round(math.sqrt(2*c*float(d)/h)))))
print(','.join(value))

18,22,24

​

7. 2-dimensional array

Write a program which takes 2 digits, X,Y as input and generates a 2-dimensional array. The element value in the i-th row and j-th column of the array should be ij.
Note: i=0,1.., X-1; j=0,1..., Y-1.
Example
Suppose the following inputs are given to the program:
i = 3, j = 5
Then, the output of the program should be:
[[0, 0, 0, 0, 0], [0, 1, 2, 3, 4], [0, 2, 4, 6, 8]]
first row = 0(0|1|2|3|4)
second row = 1*(0|1|2|3|4)

def toArray(row, col):
    multilist = [[0 for i in range(col)] for j in range(row)]
    for i in range(row):
        for j in range(col):
            multilist[i][j] = i * j
    print(multilist)

toArray(3, 5)

[[0, 0, 0, 0, 0], [0, 1, 2, 3, 4], [0, 2, 4, 6, 8]]

Explanation and some extra thinking https://spapas.github.io/2016/04/27/python-nested-list-comprehensions/

# In fact [[0 for i in range(col)] for j in range(row)] = the following code
# first draw the column
hehehe = []
hehe = []
for col in range(x):
    hehe.append(0)
# then repeat the column to draw the whole array
for row in range(y):
    hehehe.append(hehe)
hehehe

[[0, 0, 0], [0, 0, 0], [0, 0, 0], [0, 0, 0]]

# However the list comprehension normally takes the following form
non_flat = [ [1,2,3], [4,5,6], [7,8] ]
# the first for is the outer for, the next is the inner
print([y for x in non_flat for y in x])
for x in non_flat:
    for y in x:
        y
# see another example here : exclude all the lists of length < 2
print([ y for x in non_flat if len(x) > 2 for y in x ])
# equals to
for x in non_flat:
    if len(x) > 2:
        for y in x:
            y
# it's really important to see the last for as the innermost for

[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6]

# another somewhat complicate example, read from rightmost for = print all the letters and corresponding index for words of length > 2 
strings = [ ['foo', 'bar'], ['baz', 'taz'], ['w', 'koko'] ]
[ (letter, idx) for idx, lst in enumerate(strings) for word in lst if len(word)>2 for letter in word]

[('f', 0),
 ('o', 0),
 ('o', 0),
 ('b', 0),
 ('a', 0),
 ('r', 0),
 ('b', 1),
 ('a', 1),
 ('z', 1),
 ('t', 1),
 ('a', 1),
 ('z', 1),
 ('k', 2),
 ('o', 2),
 ('k', 2),
 ('o', 2)]

8. Sort a list

Take a comma separated sequence of words as input and prints the words in a comma-separated sequence after sorting them alphabetically.

Input:
without,hello,bag,world

Output:
bag,hello,without,world

words = "without,hello,bag,world".split(',')
# sorted(words) doesn't change words but return a new list, so it's better
print(sorted(words))
print(words)
# sort() returns None and changes the list in place
words.sort()
print(words)

['bag', 'hello', 'without', 'world']
['without', 'hello', 'bag', 'world']
['bag', 'hello', 'without', 'world']

sorted(words) doesn't change words but return a new list, so it's better

9. Capitalization

Take a sequence of lines as input and prints the lines capitalized.

Input:

Hello world

Practice makes perfect

Output:

HELLO WORLD

PRACTICE MAKES PERFECT

lines = []
while True:
    s = input("put some lines here")
    if s:
        lines.append(s.upper())
    else:
        break;

for sentence in lines:
    print(sentence)

put some lines heress
put some lines heresss
put some lines here
SS
SSS

Nothing complicated.
The interesting thing here is how to use while to keep asking inputs.

10. Move duplicates

Take a sequence of whitespace separated words as input and prints the words after removing all duplicate words and sorting them alphanumerically.

Input:
hello world and practice makes perfect and hello world again

output:
again and hello makes perfect practice world

words = "hello world and practice makes perfect and hello world again"
wordsList = words.split(" ")
sorted(set(wordsList))

['again', 'and', 'hello', 'makes', 'perfect', 'practice', 'world']

The key thing is to understant the difference between list and set (no duplicates in set).