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1. Booleans, Relational and Logic Operators, and Conditionals (if statements)
2. Sequences, Indexing and Slicing
3. Functions

1 Booleans, Relational and Logic Operators, and Conditionals

Discussion 1: Booleans

D1: What is “Boolean”? What values does it store? Can other types be converted to it?

# ints -> bool
# print(bool(0))  # 0 converts to False
# print(bool(1))  # all other values convert to True

# floats -> bool
# print(bool(0.0))    # 0.0 converts to False
# print(bool(3.1415)) # all other values convert to True

# str -> bool
# print(bool(""))     # empty string converts to False
# print(bool(" "))    # all other values convert to True
# print(bool("Hi!"))  # all other values convert to True

Discussion 2: Relational and Logical Operators

D2: For each of the following, identify whether it is: (a) a Boolean value; (b) a relational operator; or (c) a logical operator.

1. ==:
2. !=:
3. or:
4. True:
5. >:
6. and:
7. >=:
8. <:
9. False:
10. <=:
11. not:

📝 Operators

• the following is ordered from Highest to Lowest precedence
• Arithmetic Operators
  • () brackets
  • ** exponent
  • % modulus/remainder
  • // floor/integer division
  • / division
  • * multiplication
  • - subtraction (also a unary operator; make number negative)
  • + addition (also a unary operator; make number positive)
• Relational Operators
  • compare two values to produce a truth (boolean) result
  • == equal to
  • != not equal to
  • < less than
  • > greater than
  • <= less than or equal to
  • >= more than or equal to
  • in
• Logical Operators
  • combine Boolean values to return a single truth value
  • not
  • and
  • or

Discussion 3: Conditionals

D3: How do we use an if statement? What are the variants? How do we know what is contained inside it and what is after?

📝 if...elif...else Structure

if <condition_1>:
  <statements/operations to be executed if condition1 is True>
elif <condition_2>:
  <statements/operations to be executed if condition2 is True>
...
elif <condition_x>:
  <statements/operations to be executed if conditionx is True>
else:
  <statements/operations to be executed if all conditions are False>

Exercise 1

E1: Evaluate the following truth expressions:

1. True or False:
2. True and False:
3. False and not False or True:
4. False and (not False or True):

📝 Logical Operator Truth Tables

Exercise 2

E2: For each of the following if statements, give an example of a value for var which will trigger it and one which will not.

1. [object Object]

2. [object Object]

3. [object Object]

4. [object Object]

Exercise 3

E3: What’s wrong with this code? How can you fix it?

letter = input("Enter a letter: ")
if letter == 'a' or 'e' or 'i' or 'o' or 'u':
    print("vowel")
else:
    print("consonant")

Exercise 4 (assignment VS equality)

E4: What’s wrong with this code? How can you fix it?

eggs == 3
if eggs = 5:
    print("spam")
else:
    print("not spam")

2 Sequences, Indexing and Slicing

Discussion 4: Sequences

D4: What is a “Sequence”? What sequences have we seen so far? What operators can we use with sequences?

📝 Sequence Operations

# Create copies of sequences with *
# print("hello"*2)
# print(("python", 2, [1, 2])*4)  # tuples and lists are sequences too (later)

# Concatenate sequences with +
# print("good " + "afternoon")

# Use for...in... to loop through sequences (later)
# for letter in "awesome":
#     print(letter)

Discussion 5: Indexing

D5: What is indexing? How can you do it?

Dicussion 6: Slicing

D6: What is slicing? How can you do it?

Exercise 5

• length: 6
• Slicing: [start:end:step]

E5: Evaluate the following given the assignment s = "python"

1. s[1]:
2. s[-1]:
3. s[1:3] + s[3:5]:
4. s[10]:
5. s[10:]:
6. s[-4:-2]:
7. s[:-4]:
8. s[::2]:
9. s[::-1]:

# only use the code block for checking your answers!

3 Functions

Discussion 7: Functions

D7: What is a “function”? How do we call (use) one? How do we define one ourselves?

📝 Function (and Docstring) Structure

CONSTANT = 0 # declare constants before all functions
def <function-name>(<parameters>):
    """
    docstring describing what the function does.
    """
    <function-body>

def sum(x, y):
    """Returns the sum of two integers."""
    return x + y

sum(1, 2)   # function call
# print(sum(1, 2))    # printing the returned value

# Viewing Docstrings
# print(sum.__doc__)
# print(print.__doc__)  # built-in functions also have docstrings

• Ways to structure docstrings

  • short and sweet one-liners

    • example:

      def multiplier(a, b):
          """Takes in two numbers, returns their product."""
          return a*b
      

  • detailed params/args, returns, raises, example

    • examples:

      def add_binary(a, b):
          """
          Returns the sum of two decimal numbers in binary digits.
      
          Parameters
          ----------
          a (int): A decimal integer
          b (int): Another decimal integer
      
          Returns
          -------
          binary_sum (str): Binary string of the sum of a and b
          """
          #...
      

• PEP257 - Docstring Conventions

• What are the most common Python docstring formats? [closed] | stackoverflow

Discussion 8: Return

D8: What does it mean to “return” a value from a function and why would we want to? Does a function always need a return value?

def example_1():
    return 1
    print("abc")
    return 2
    return 3

print(example_1)    # what do you think this will return?

Discussion 9: Function of Functions

D9: Why should we use functions? Could we live without functions?

Discussion 10: Brackets and Functions

D10: Why are brackets important when calling a function? Are they needed even if it takes no arguments?

Exercise 6

E6: What’s wrong with this code? How can you fix it?

def calc(n1, n2):
    answer = n1 + (n1 * n2)
    print(answer)

num = int(input("Enter the second number: "))
result = calc(2, num)
print("The result is:", result)

Coding Problems

Problem 1

"""
P1: Write a function which takes a string as a single argument, and returns a
shortened version of the string consisting of its first three letters and then
every second letter in the rest of the word. shorten('uncalled') should return
'uncle'.
"""

Problem 2

"""
P2: Write a function which takes a sentence as a single argument (in the form of
a string), and evaluates whether it is valid based on whether the first letter is
capitalised and the last character is a full stop. It should return a Boolean
value True or False.
"""

Problem 3

"""
P3: Write a program which asks the user for two numbers and an operator out of
+, -, / and * and performs that operation on the two numbers, printing the
result.
"""