Conditionals and Loops¶

if, elif and else and Indentation¶

In [1]:

# 1. if, elif, else and Indentation
x = 15

if x < 10:
    print("Less than 10")
elif x == 10:
    print("Equal to 10")
else:
    print("Greater than 10")

# 1. if, elif, else and Indentation x = 15 if x < 10: print("Less than 10") elif x == 10: print("Equal to 10") else: print("Greater than 10")

Greater than 10

In [2]:

if x < 10:
    print('x less than 10')
print('x less than 10')

if x < 10: print('x less than 10') print('x less than 10')

x less than 10

Conditional statement using logical operator (and, or, not)¶

In [3]:

# 2. Logical Operators: and, or, not
a = 5
b = 10

if a < 10 and b > 5:
    print("Both conditions are True")

if a > 10 or b > 5:
    print("At least one condition is True")

if not a > 10:
    print("a is not greater than 10")

# 2. Logical Operators: and, or, not a = 5 b = 10 if a < 10 and b > 5: print("Both conditions are True") if a > 10 or b > 5: print("At least one condition is True") if not a > 10: print("a is not greater than 10")

Both conditions are True
At least one condition is True
a is not greater than 10

Identity(is) vs Equality(==)¶

In [4]:

# 3. is vs. == (Identity vs. Equality)
x = [1, 2, 3]
y = [1, 2, 3]
z = x

print(x == y)  # True: Same content
print(x is y)  # False: Different objects
print(x is z)  # True: Same object

# 3. is vs. == (Identity vs. Equality) x = [1, 2, 3] y = [1, 2, 3] z = x print(x == y) # True: Same content print(x is y) # False: Different objects print(x is z) # True: Same object

True
False
True

In [5]:

id(x), id(y), id(z)

id(x), id(y), id(z)

Out[5]:

(136234817650112, 136234817650496, 136234817650112)

Ternary Operator¶

• The ternary operator in Python allows us to perform conditional checks and assign values or perform operations on a single line.

x = a if condition else b

In [6]:

n = 5
res = "Even" if n % 2 == 0 else "Odd"
print(res)

n = 5 res = "Even" if n % 2 == 0 else "Odd" print(res)

Odd

1. Check Even or Odd¶

Write a program that takes an integer input from the user and checks if it is even or odd.

2. Check Age Category¶

Write a program that asks for a person's age and prints:

• "Child" if age < 13
• "Teenager" if 13 <= age < 20
• "Adult" if age >= 20

3. Write a one-liner using a ternary operator to assign a grade based on a student's score.¶

Given a variable score (an integer from 0 to 100), write a one-liner to assign:

"Pass" if the score is 40 or above

"Fail" if the score is below 40

Loops¶

In [7]:

cities_list = ('Kathmandu', 'Lalitpur', 'Bhaktapur', 'asdf')

for city in cities_list:
    print(city.lower())
    print(city.upper())

cities_list = ('Kathmandu', 'Lalitpur', 'Bhaktapur', 'asdf') for city in cities_list: print(city.lower()) print(city.upper())

kathmandu
KATHMANDU
lalitpur
LALITPUR
bhaktapur
BHAKTAPUR
asdf
ASDF

In [8]:

word = 'Kathmandu'

for char in word:
    print(char)

word = 'Kathmandu' for char in word: print(char)

K
a
t
h
m
a
n
d
u

In [9]:

# 4. Introduction to Loops: for and while
# for loop
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# 4. Introduction to Loops: for and while # for loop fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit)

apple
banana
cherry

In [10]:

# while loop
count = 0
while count < 3:
    print("Count:", count)
    count += 1

# while loop count = 0 while count < 3: print("Count:", count) count += 1

Count: 0
Count: 1
Count: 2

In [11]:

for i in range(10):
    print(i)

for i in range(10): print(i)

0
1
2
3
4
5
6
7
8
9

In [12]:

for i in range(2, 10):
    print(i)

for i in range(2, 10): print(i)

2
3
4
5
6
7
8
9

In [13]:

for i in range(2, 10, 2):
    print(i)

for i in range(2, 10, 2): print(i)

2
4
6
8

In [14]:

for i in range(10, 1, -2):
    print(i)

for i in range(10, 1, -2): print(i)

10
8
6
4
2

In [15]:

numbers_list = []
for i in range(1, 101):
    numbers_list.append(i)

numbers_list = [] for i in range(1, 101): numbers_list.append(i)

In [16]:

nums_list = list(range(1, 101))

nums_list = list(range(1, 101))

In [17]:

numbers_list = [1, 2, 3, 4, 5, 6, 7,]

numbers_list = [1, 2, 3, 4, 5, 6, 7,]

In [18]:

# 5. Loop control: break, continue, pass
# break example
for i in range(5):
    if i == 3:
        break
    print(f"Break example: {i}")

# 5. Loop control: break, continue, pass # break example for i in range(5): if i == 3: break print(f"Break example: {i}")

Break example: 0
Break example: 1
Break example: 2

In [19]:

# continue example
for i in range(5):
    if i == 2:
        continue
    print("Continue example:", i)

# continue example for i in range(5): if i == 2: continue print("Continue example:", i)

Continue example: 0
Continue example: 1
Continue example: 3
Continue example: 4

Range¶

range(start, stop, step)

In [20]:

# range()
for i in range(1, 6):
    print(i)

# range() for i in range(1, 6): print(i)

1
2
3
4
5

In [21]:

for i in range(1, 10, 2):
    print(i)

for i in range(1, 10, 2): print(i)

1
3
5
7
9

In [22]:

for i in range(10, 1, -1):
    print(i)

for i in range(10, 1, -1): print(i)

10
9
8
7
6
5
4
3
2

Enumerate¶

enumerate(iterable, start) 

default value for start = 0

In [23]:

colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(f"{index} : {color}")

colors = ["red", "green", "blue"] for index, color in enumerate(colors): print(f"{index} : {color}")

0 : red
1 : green
2 : blue

In [24]:

colors = ["red", "green", "blue"]
for index, color in enumerate(colors, start=2):
    print(f"{index} : {color}")

colors = ["red", "green", "blue"] for index, color in enumerate(colors, start=2): print(f"{index} : {color}")

2 : red
3 : green
4 : blue

In [25]:

# enumerate()
colors = ["red", "green", "blue"]
for index, color in enumerate(colors):
    print(f"Index {index} has color {color}")

# enumerate() colors = ["red", "green", "blue"] for index, color in enumerate(colors): print(f"Index {index} has color {color}")

Index 0 has color red
Index 1 has color green
Index 2 has color blue

Exercise¶

3. Print Multiplication Table (for loop)¶

Print the multiplication table of a number entered by the user (from 1 to 10). Print in the following format. Use f-string in this case

Input = 2

Output:

2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
....
...

2 * 10 = 20

4. Sum of First N Numbers (while loop)¶

Ask the user for a number n and compute the sum of the first n natural numbers using a while loop.

Input : 5

Output : 15

5. Write a program that takes a string input from the user and uses a dictionary to count how many times each character appears in the string. Use a loop to iterate over the string.¶

Example:

Input: "banana"

Output:

{'b': 1, 'a': 3, 'n': 2}

6. Filter out All Even Numbers in a List¶

Write a program that takes a list of integers and uses a loop to create a new list containing only the even numbers from the original list. Then print the new list.

Example:

Input: [1, 4, 7, 8, 10, 3, 6]

Output:
[4, 8, 10, 6]

In [26]:

input_list = [1, 23, 983, 2923, 83, 85, 98, 20, 1]
output_list = []
for num in input_list:
    if num % 2 == 0:
        output_list.append(num)

print(output_list)

input_list = [1, 23, 983, 2923, 83, 85, 98, 20, 1] output_list = [] for num in input_list: if num % 2 == 0: output_list.append(num) print(output_list)

[98, 20]

In [27]:

word = 'banana'
counter_dictionary = {}

for char in word:
    if char not in counter_dictionary:
        counter_dictionary[char] = 1
    elif char in counter_dictionary:
        counter_dictionary[char] += 1

print(counter_dictionary)

word = 'banana' counter_dictionary = {} for char in word: if char not in counter_dictionary: counter_dictionary[char] = 1 elif char in counter_dictionary: counter_dictionary[char] += 1 print(counter_dictionary)

{'b': 1, 'a': 3, 'n': 2}

In [28]:

'cocot' in ['apple', 'fruites', 'coco', 'mike']

'cocot' in ['apple', 'fruites', 'coco', 'mike']

Out[28]:

False

List Comprehension¶

In [29]:

numbers = [3, 6, 8, 9, 2]

output_list = []
for number in numbers:
    output_list.append(number ** 2)

numbers = [3, 6, 8, 9, 2] output_list = [] for number in numbers: output_list.append(number ** 2)

In [30]:

numbers = [3, 6, 8, 9, 2]

output_list = [number**2 for number in numbers]
print(output_list)

numbers = [3, 6, 8, 9, 2] output_list = [number**2 for number in numbers] print(output_list)

[9, 36, 64, 81, 4]

In [31]:

print(output_list)

print(output_list)

[9, 36, 64, 81, 4]

Exercise¶

1. Given a list of words, create a list with each word capitalized. Use List Comprehension.¶

Note: Use string.title() function to capitalize

input_word_list = ['apple', 'banana', 'coco']

output_word_list = ['Apple', 'Banana', 'Coco]

2. Generate pairs of numbers (i, j) where i and j are from 1 to 10, but only where i < j. Use List Comprehension¶

Input: [(2, 5), (5, 2), (3, 7), (8, 2)]

Output : [(2, 5), (3, 7)]

In [32]:

input_list = [(2, 5), (5, 2), (3, 7), (8, 2)]

output_list = []
for pair in input_list:
    if pair[0] < pair[1]:
        output_list.append(pair)

print(output_list)

input_list = [(2, 5), (5, 2), (3, 7), (8, 2)] output_list = [] for pair in input_list: if pair[0] < pair[1]: output_list.append(pair) print(output_list)

[(2, 5), (3, 7)]

In [33]:

input_list = [(2, 5), (5, 2), (3, 7), (8, 2)]


[pair for pair in input_list if pair[0] < pair[1]]

input_list = [(2, 5), (5, 2), (3, 7), (8, 2)] [pair for pair in input_list if pair[0] < pair[1]]

Out[33]:

[(2, 5), (3, 7)]