Cheatsheets
Analyze Financial Data with Python - Introduction to Python

Analyze Financial Data with Python - Introduction to Python

Getting Started

Adding Comments

Comments are notes you add to your code to explain what it does. They don't affect the program's operation but help you and others understand the code better.

                                

# This is a comment explaining the next line of code
user = "JDoe"  # Comment after code

Basic Math Operations

You can perform basic arithmetic like addition, subtraction, multiplication, and division in Python. These are done using symbols like +, -, *, and /.

                                

# Simple math operations
result = 10 + 30  # Addition
result = 40 - 10  # Subtraction
result = 50 * 5   # Multiplication
result = 16 / 4   # Division
result = 25 % 2   # Modulo (remainder)
result = 5 ** 3  # Exponentiation (5 raised to the power of 3)

Using += to Update Values

The += operator adds a value to an existing variable. It makes the code shorter and easier to read. It can also be used to join strings together.

                                

# Using += to update a number
counter = 0
counter += 10  # Same as counter = counter + 10
# Using += to concatenate strings
message = "Part 1"
message += " and Part 2"

Creating and Using Variables

Variables are like containers that hold data. You can change what data they hold by assigning new values to them. You can use names that are easy to remember for these containers.

                                

# Example of variables
user_name = "codey"
user_id = 100
verified = False
# Changing the value of a variable
points = 100
points = 120

Finding Remainders with %

The % symbol gives you the remainder after dividing one number by another. It's useful for checking if a number is divisible by another number.

                                

# Finding remainders
remainder1 = 8 % 4  # Remainder is 0
remainder2 = 12 % 5  # Remainder is 2

Understanding Whole Numbers

Whole numbers, or integers, are numbers without any fractions or decimals. They can be positive, negative, or zero.

                                

# Whole numbers
chairs = 4
tables = 1
broken_chairs = -2
sofas = 0
# Decimal numbers (not integers)
lights = 2.5
left_overs = 0.0

Joining Strings Together

You can join (concatenate) strings using the + operator. Strings are sequences of characters, like words or sentences.

                                

# Joining strings
first = "Hello"
second = "World"
result = first + " " + second  # Result is "Hello World"

Common Errors in Code

Sometimes, mistakes in code can cause errors. Python will show you where it found the mistake, like a misplaced symbol or typo.

                                

# Example of a syntax error
if False ISNOTEQUAL True:
                  ^
SyntaxError: invalid syntax

Division by Zero Error

Dividing any number by zero is not allowed and causes an error. Python reports this as a ZeroDivisionError.

                                

# Example of division by zero
numerator = 100
denominator = 0
result = numerator / denominator
ZeroDivisionError: division by zero

Working with Text Strings

Strings are sequences of characters. They can be enclosed in single or double quotes, and can span multiple lines if needed.

                                

# Examples of strings
user = "User Full Name"
game = 'Monopoly'
long_string = "This string is broken up \
over multiple lines"

Mistakes in Assignments

You can't use the + operator to assign values. The + operator is for addition or concatenation, not for assignment.

                                

age = 7 + 5 = 4
File "", line 1
SyntaxError: can't assign to operator

Handling Missing Variables

If you try to use a variable that hasn't been defined, Python will show an error. This helps you find and fix typos or missing code.

                                

# Example of using an undefined variable
misspelled_variable
NameError: name 'misspelled_variable' is not defined

Working with Decimal Numbers

Decimal numbers, or floats, include a fraction part, like 3.14. They are used when you need more precision than whole numbers.

                                

# Example of decimal numbers
pi = 3.14159
meal_cost = 12.99
tip_percent = 0.20

Displaying Output with print()

The print() function shows information on the screen. You can print text, numbers, or results from calculations.

                                

print("Hello World!")  # Displays text
print(100)  # Displays a number
pi = 3.14159
print(pi)  # Displays the value of a variable

Functions

Simple Anonymous Functions

A lambda function is a quick, unnamed function you can use for simple operations. It's handy for tasks like mapping or filtering data in one line.

                                

# Syntax for a lambda function
lambda x: x + 1

Using Lambda Functions

Lambda functions can take inputs (arguments) to perform a task. They are used for short, one-off functions where a full function definition isn't necessary.

                                

# Example of a lambda function
add = lambda x, y: x + y
print(add(5, 3))  # Output: 8

Function Parameters

Parameters are placeholders in a function that hold the values you pass to it. They let the function know what data to work with.

                                

# Example function with parameters

def greet(name):
  print("Hello, " + name)

greet("Alice")  # Output: Hello, Alice

Using Multiple Inputs

Functions can take multiple parameters. This allows them to handle more complex tasks by providing several pieces of information.

                                

# Function with multiple parameters

def prepare_for_school(backpack, pencil_case):
  if backpack == 'full' and pencil_case == 'full':
    print("Ready for school!")

prepare_for_school('full', 'full')  # Output: Ready for school!

Creating Functions

Functions in Python can be created with the def keyword and can have parameters. They let you write reusable code to perform specific tasks.

                                

# Defining and using a function

def add_one(x):
  return x + 1

print(add_one(2))  # Output: 3
print(add_one(5))  # Output: 6

Indentation in Functions

Python uses indentation to define the blocks of code that belong to a function. Proper indentation is crucial for defining what code is inside the function.

                                

# Example of indentation

def calculate_sum(number):
  sum = 0
  for x in range(number):
    sum += x
  return sum

print(calculate_sum(5))  # Output: 10

Calling Functions

You call a function by writing its name followed by parentheses. This allows you to execute the function's code whenever needed.

                                

# Calling a function

def say_hello():
  print("Hello, world!")

say_hello()  # Output: Hello, world!

Function Results

Functions can return a value using the return keyword. This lets you use the result of the function in other parts of your program.

                                

# Function that returns a value

def describe_item(store, item, price):
  return store + " is selling " + item + " for " + price

print(describe_item("The Market", "apples", "$2"))  # Output: The Market is selling apples for $2

Keyword Arguments in Functions

When calling a function, you can specify arguments by name, allowing you to pass them in any order. Default values can be provided for parameters.

                                

# Using keyword arguments

def volume(length=1, width=1, depth=1):
  return length * width * depth

print(volume(length=2, width=3, depth=4))  # Output: 24

Returning Multiple Results

A function can return more than one value. These values can be captured and used individually.

                                

# Function returning multiple values

def square_numbers(x, y, z):
  return x*x, y*y, z*z

squared = square_numbers(3, 4, 5)
print(squared)  # Output: (9, 16, 25)

Variable Scope in Functions

Variables in functions are local to the function unless specified otherwise. This means they only exist within the function’s code block.

                                

# Example of variable scope

def my_function():
  a = 10
  print(a)  # Output: 10

my_function()
print(a)  # Error: a is not defined outside the function

Using Global Variables

Global variables are accessible from anywhere in the code, not just inside functions. You can use them across different functions.

                                

# Example of global variable

a = "Hello"

def print_message():
  print(a)  # Output: Hello

print_message()

Local Variables in Functions

Parameters in functions act as local variables. They only exist within the function and can be used only there.

                                

# Example of local variable

def display_value(value):
  print(value)

display_value(7)  # Output: 7

print(value)  # Error: value is not defined outside the function

Making Decisions

Working with Lists

Loops

Stopping a Loop Early

In a loop, the `break` keyword stops the loop immediately, no matter where you are in the loop. After the loop stops, the program continues with the code that follows it.

                                

numbers = [0, 254, 2, -1, 3]
for num in numbers:
  if num < 0:
    print("Negative number detected!")
    break
  print(num)
  # Output:
  # 0
  # 254
  # 2
  # Negative number detected!

Creating Lists with List Comprehension

List comprehension is a quick way to create lists. It uses brackets with an expression and a `for` loop to generate a new list. Here, it creates a list of squares for even numbers between 0 and 9.

                                

# Create a list of squares for even numbers from 0 to 9
result = [x**2 for x in range(10) if x % 2 == 0]
print(result)
# Output: [0, 4, 16, 36, 64]

Using a For Loop

A `for` loop is used to repeat actions for each item in a list. The loop goes through each item one by one and performs the actions inside the loop.

                                

# Print each number in the list
nums = [1, 2, 3, 4, 5]
for num in nums:
  print(num)
# Output:
# 1
# 2
# 3
# 4
# 5

Skipping Parts of a Loop

The `continue` keyword in a loop skips the rest of the code inside the loop for that iteration and moves on to the next iteration. Here, it skips printing negative numbers.

                                

big_number_list = [1, 2, -1, 4, -5, 5, 2, -9]
# Print only positive numbers:
for i in big_number_list:
  if i < 0:
    continue
  print(i)
# Output:
# 1
# 2
# 4
# 5
# 2

Using `range()` with Loops

`range()` generates a sequence of numbers, which can be used in a loop to repeat actions a specific number of times.

                                

# Print numbers 0, 1, 2
for i in range(3):
  print(i)
# Print "WARNING" 3 times
for i in range(3):
  print("WARNING")
# Output:
# 0
# 1
# 2
# WARNING
# WARNING
# WARNING

Running a Loop Indefinitely

An infinite loop keeps running until you manually stop it or it meets a stopping condition. Here, a loop runs once because it sets `hungry` to `False` after the first iteration.

                                

# This loop will only run once
hungry = True
while hungry:
  print("Time to eat!")
  hungry = False
# This loop will run 5 times

i = 1
while i < 6:
  print(i)
  i = i + 1
# Output:
# Time to eat!
# 1
# 2
# 3
# 4
# 5

Using Nested Loops

Nested loops have one loop inside another. They are used to perform actions on items within items, such as names within groups. Each loop works through its set of actions separately.

                                

groups = [["Jobs", "Gates"], ["Newton", "Euclid"], ["Einstein", "Feynman"]]
# Loop through each group and each name within the group
for group in groups:
  for name in group:
    print(name)
# Output:
# Jobs
# Gates
# Newton
# Euclid
# Einstein
# Feynman

Programming Cheatsheets: Quick Reference for Productivity

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