CS250: Python for Data Science

Functions

Here's what you should have seen in your REPL:

>>> add_numbers(1, 2)
3
# Let's use the string formatting we learned in the last chapter
>>> print(f"The sum of 1 and 2 is {add_numbers(1, 2)}")
The sum of 1 and 2 is 3

Function Scope

Here's what you should have seen in your REPL:

>>> x = 1
>>> y = 2
>>> def add_numbers(x, y):
...     print(f"Inside the function, x = {x} and y = {y}")
...     return x + y
...
>>> print(f"Outside the function, x = {x} and y = {y}")
Outside the function, x = 1 and y = 2
>>>
>>> print(f"The sum of 5 and 6 is {add_numbers(5, 6)}")
Inside the function, x = 5 and y = 6
The sum of 5 and 6 is 11

Positional Arguments vs Keyword Arguments

Here's what you should have seen in your REPL:

>>> def calculate_numbers(x, y, operation="add"):
...     if operation == "add":
...         return x + y
...     elif operation == "subtract":
...         return x - y
...
# Let's try our new function. Remember, if we don't pass the operation keyword argument, the default is "add"
>>> calculate_numbers(2, 3)
5
# You can pass a keyword argument as a normal positional argument
>>> calculate_numbers(2, 3, "subtract")
-1
# You can also use the argument's keyword. This helps with readability
>>> calculate_numbers(2, 3, operation="subtract")
-1

Boolean Logic

Comparisons

Here's what you should have seen in your REPL:

>>> 10 > 5
True
>>> 5 > 10
False
>>> 10 > 10
False
>>> 10 >= 10
True
>>> 5 < 10
True
>>> 5 < 5
False
>>> 5 <= 5
True
>>> 5 == 5
True
>>> 5 != 10
True

Truthiness

Here's what you should have seen in your REPL:

>>> 5 == True
False
>>> # The number 5 does not equal True, but...
>>> if 5:
...     print("The number 5 is truthy!")
...
The number 5 is truthy!
>>> # The number 5 is truthy for an if test!

>>> 1 == True
True
>>> 0 == False
True

Boolean Operators

Here's what you should have seen in your REPL:

>>> a = False
>>> b = False
>>> c = False
>>> a or b or c
False
>>> b = True
>>> a or b or c
True

>>> a and b and c
False
>>> a = True
>>> c = True
>>> a and b and c
True

>>> a = False
>>> b = False
>>> not a
True
>>> a and not b
False

Control statements and looping

if, else, and elif

Here's what you should have seen in your REPL:

>>> def test_number(number):
...     if number < 100:
...         print("This is a pretty small number")
...     elif number == 100:
...         print("This number is alright")
...     else:
...         print("This number is huge!")
...
>>> test_number(5)
This is a pretty small number
>>> test_number(99)
This is a pretty small number
>>> test_number(100)
This number is alright
>>> test_number(8675309)
This number is huge!

>>> def fizzbuzz(number):
...     if number % 3 == 0 and number % 5 == 0:
...         print("Fizzbuzz!")
...
>>> fizzbuzz(3)
>>> fizzbuzz(5)
>>> fizzbuzz(15)
Fizzbuzz!

>>> def my_func(my_list):
...     if my_list:
...         for item in my_list:
...             if item is None:
...                 print("Got None!")
...             else:
...                 print(item)
...     else:
...         print("Got an empty list!")
...
>>> my_func([1, 2, 3])
1
2
3
>>> my_func([2, None, "hello", 42])
2
Got None!
hello
42
>>> my_func([])
Got an empty list!

The for loop, range() and enumerate()

Here's what you should have seen in your REPL:

>>> my_list = [1, 2, 3]
>>> for num in my_list:
...     print(f"Next value: {num}")
...
Next value: 0
Next value: 1
Next value: 2

>>> for num in range(0, 3):
...     print(f"Next value: {num}")
...
Next value: 0
Next value: 1
Next value: 2

>>> my_list = ["foo", "bar", "baz"]
>>> for index, item in enumerate(my_list):
...     print(f"Item {index}: {item}")
...
Item 0: foo
Item 1: bar
Item 2: baz

>>> my_dict = {"foo": "bar", "hello": "world"}
>>> for key in my_dict:
...     print(f"Key: {key}")
...
Key: foo
Key: hello

>>> for key in my_dict.keys():
...     print(f"Key: {key}")
...
Key: foo
Key: hello

>>> for value in my_dict.values():
...     print(f"Value: {value}")
...
Value: bar
Value: world

>>> for key, value in my_dict.items():
...     print(f"Item {key} = {value}")
...
Item foo = bar
Item hello = world

return

Here's what you should have seen in your REPL:

>>> def is_number_in_list(number_to_check, list_to_search):
...     for num in list_to_search:
...         print(f"Checking {num}...")
...         if num == number_to_check:
...             return True
...     return False
...
>>> is_number_in_list(27, my_list)
Checking 1...
Checking 2...
Checking 3...
Checking 4...
Checking 5...
False
>>> is_number_in_list(2, my_list)
Checking 1...
Checking 2...
True

while loop

Here's what you should have seen in your REPL:

>>> counter = 0
>>> while counter < 3:
...     print(f"Counter = {counter}")
...     counter += 1
...
Counter = 0
Counter = 1
Counter = 2

>>> counter = 0
>>> while True:
...     print(f"Counter = {counter}")
...     if counter == 3:
...         break
...     counter += 1
...
Counter = 0
Counter = 1
Counter = 2
Counter = 3

Nested Loops

Here's what you should have seen in your REPL:

>>> for x in range(0, 5):
...     for y in range(0, 5):
...         print(f"x = {x}, y = {y}")
...         if y == 2:
...             break
...
x = 0, y = 0
x = 0, y = 1
x = 0, y = 2
x = 1, y = 0
x = 1, y = 1
x = 1, y = 2
x = 2, y = 0
x = 2, y = 1
x = 2, y = 2
x = 3, y = 0
x = 3, y = 1
x = 3, y = 2
x = 4, y = 0
x = 4, y = 1
x = 4, y = 2