Module 00 · Foundation

A short Python bridge

Read the small amount of Python needed to begin the pandas lessons.

Before you start: No programming experience is required; work through one line at a time.

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M00C01 · Explore · predict · practice

Names hold values

A variable is a name associated with a value. The equals sign assigns a value; two equals signs compare values. Quotation marks make text, while an unquoted number can take part in arithmetic. print() displays a value so you can inspect it.

ReadWhich line assigns a value, and which line compares two values?

PredictWhat will next_age print? Will age itself become 21?

ExplainWhy are "20" and 20 different?

Read the example

name = "Amira"
age = 20
next_age = age + 1
is_twenty = age == 20
print(name)
print(next_age)
print(is_twenty)
print(type(age).__name__)

Verified example output · pandas 2.2.3

Amira
21
True
int

Watch for this. Python names are case-sensitive: age and Age are different names.

Your turn

Describe Bilal, age 21, using name and age. Calculate his age in three years in next_age. Store the comparison of his current age with 21 in is_twenty_one, then print the results.

For the code check, keep these result variable names: age, is_twenty_one, name, next_age. Different valid approaches are welcome.

Your Python code

name = "Amira"
age = 20
next_age = age + 1
is_twenty = age == 20
print(name)
print(next_age)
print(is_twenty)
print(type(age).__name__)

Show a hint

Change the name and starting age, then use age + 3. Keep = for assignment and == for comparison.

Show one worked solution

name = "Bilal"
age = 21
next_age = age + 3
is_twenty_one = age == 21
print(name)
print(next_age)
print(is_twenty_one)

The results are Bilal, 24, and True. The original age remains 21.

Compare your explanations

Read. age = 20 assigns 20 to age. The expression age == 20 compares age with 20 and produces True.
Predict. next_age prints 21. age stays 20 because the calculated value was assigned to a different name.
Explain. "20" is text; 20 is a whole number. Their types determine which operations make sense.

One quick check

What does age == 20 do?

What you should be able to explain. I can distinguish a value, a variable, an assignment, and a comparison.

Your own assessment, separate from code checks

M00C02 · Explore · predict · practice

A list keeps values in order

Square brackets create a list. Each value has a position, beginning at 0. len() counts the values, and a slice selects a range of positions. A slice includes its start position and excludes its stop position.

ReadWhat is the difference between scores and scores[0]?

PredictDoes scores[0:2] contain two values or three?

ExplainWhy would scores[3] fail for this list?

Read the example

scores = [88, 72, 91]
first_score = scores[0]
first_two = scores[0:2]
print(first_score)
print(first_two)
print(len(scores))

Verified example output · pandas 2.2.3

88
[88, 72]
3

Watch for this. A list position is an integer. The text "0" is not the same as position 0.

Your turn

Select the second and third scores into result. Then add 65 to the end of scores using append(), and print the new list length.

For the code check, keep these result variable names: result, scores. Different valid approaches are welcome.

Your Python code

scores = [88, 72, 91]
first_score = scores[0]
first_two = scores[0:2]
print(first_score)
print(first_two)
print(len(scores))

Show a hint

Use the slice [1:3], then scores.append(65).

Show one worked solution

scores = [88, 72, 91]
result = scores[1:3]
scores.append(65)
print(result)
print(scores)
print(len(scores))

result contains 72 and 91. The original list now has four values, ending in 65.

Compare your explanations

Read. scores is the whole list. scores[0] retrieves the first value, 88.
Predict. Two values: 88 and 72. Position 2 is excluded from the slice.
Explain. The list has three values at positions 0, 1, and 2. Position 3 does not exist, so Python raises IndexError.

One quick check

Which position refers to the first list value?

What you should be able to explain. I can count, select, and append list values.

Your own assessment, separate from code checks

M00C03 · Explore · predict · practice

Give a calculation a name

A function is a named set of instructions you can reuse. def starts a function definition, and the indented body states what it does. A parameter receives an input value when the function is called. return sends the result back so it can be saved or used in another calculation.

ReadIn add_bonus(72, 3), what values do score and bonus receive?

PredictWhat do first and second contain?

ExplainWhy return the answer instead of only printing it inside the function?

Read the example

def add_bonus(score, bonus):
    return score + bonus

first = add_bonus(72, 3)
second = add_bonus(88, 2)
print(first)
print(second)

Verified example output · pandas 2.2.3

75
90

Watch for this. Indentation is part of Python syntax. Division also requires a nonzero denominator.

Your turn

Create a function called to_percentage(points, maximum) that returns points divided by maximum, multiplied by 100. Calculate 16 out of 20 into result and print it.

For the code check, keep these result variable names: result. Different valid approaches are welcome.

Your Python code

def add_bonus(score, bonus):
    return score + bonus

first = add_bonus(72, 3)
second = add_bonus(88, 2)
print(first)
print(second)

Show a hint

Keep the return line indented. For this exercise, maximum is positive.

Show one worked solution

def to_percentage(points, maximum):
    return (points / maximum) * 100

result = to_percentage(16, 20)
print(result)

The returned percentage is 80.0. The same function can be called with a different number of points and a different positive maximum.

Compare your explanations

Read. score receives 72 and bonus receives 3 for that call.
Predict. first contains 75; second contains 90.
Explain. A returned answer can be saved in a variable and used later. Printing alone displays it but does not return that answer to the caller.

One quick check

Which keyword sends the calculated answer back to the caller?

What you should be able to explain. I can read a small function, call it, and use its returned value.

Your own assessment, separate from code checks

M00C04 · Explore · predict · practice

Import a tool and read an error

import makes a module's tools available; as gives the module a shorter name. This example uses Python's built-in math module. The try/except block catches an expected conversion error so we can read its type and message, then continue. Read the error name and the failing value before changing code.

ReadWhat does m refer to after import math as m?

PredictWhy does float("nine") raise ValueError, but float("9") works?

ExplainWhat should you inspect first when a cell reports an error?

Read the example

import math as m

try:
    number = float("nine")
except ValueError as error:
    print(type(error).__name__ + ": " + str(error))

number = float("9")
result = m.sqrt(number)
print("Corrected result:", result)

Verified example output · pandas 2.2.3

ValueError: could not convert string to float: 'nine'
Corrected result: 3.0

Watch for this. Catching an error does not repair its cause. This example prints the expected error and then supplies a valid value explicitly.

Your turn

Import math as m, set text to "25", convert text to a number, and calculate its square root in result. Print the result.

For the code check, keep these result variable names: number, result, text. Different valid approaches are welcome.

Your Python code

import math as m

try:
    number = float("nine")
except ValueError as error:
    print(type(error).__name__ + ": " + str(error))

number = float("9")
result = m.sqrt(number)
print("Corrected result:", result)

Show a hint

Use float(text) for conversion and m.sqrt(number) for the calculation.

Show one worked solution

import math as m

text = "25"
number = float(text)
result = m.sqrt(number)
print(result)

The result is 5.0. Later, import pandas as pd follows the same alias pattern; pandas supplies the data tools used in the course.

Compare your explanations

Read. m is a short name for the math module. m.sqrt accesses its square-root function.
Predict. The word nine cannot be parsed as a numeric value by float. The digit string 9 can, producing 9.0.
Explain. Read the error type, its message, and the line that failed. Check the actual input and variable names rather than changing unrelated lines.

One quick check

What does as pd mean in import pandas as pd?

What you should be able to explain. I can recognize an import alias and use an error message to guide a correction.

Your own assessment, separate from code checks

Next: Start with a dictionary

Further detail: official documentation for this topic.