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Syntax and Types

Think of this page as learning the alphabet before writing sentences. Python has a small set of core building blocks — once you know them, you can read almost any Python code you come across.

What you'll learn

  • Python's built-in types: int, float, str, bool, and None
  • How to write f-strings and use operators
  • Control flow with if, for, and while
  • Python's truthiness rules
  • How to read input and print output

Variables and Assignment

A variable is like a labeled jar you put a value in. You write the label, then an equals sign, then the value. Python figures out what kind of value it is on its own — you do not need to declare a type upfront.

name = "Alice"          # str  (text)
age = 30                # int  (whole number)
score = 9.5             # float (decimal number)
active = True           # bool (yes/no value)
result = None           # NoneType (the "nothing here" value)

You can change a variable's value at any time by assigning again. Variable names use snake_case (words joined by underscores) by convention.

Core Built-in Types

Here is a quick summary of the five types you will use most often:

Type Example Notes
int 42, -7 Whole numbers, any size
float 3.14, -0.001 Numbers with a decimal point
str "hello", 'hi' Text (the programming word is string)
bool True, False A yes/no, on/off value
None None Represents "no value" or "nothing"

You can ask Python what type a value is:

print(type(42))             # <class 'int'>
print(isinstance(42, int))  # True

Strings and f-strings

A string is just text wrapped in quotes. You can join strings together (the programming word for this is concatenation), but the modern way is to use an f-string, which lets you drop values directly into your text:

greeting = "Hello"
subject = "world"

# Joining strings the old way
message = greeting + ", " + subject + "!"

# f-string — the modern, readable way
message = f"{greeting}, {subject}!"
print(message)  # Hello, world!

# You can put expressions inside the curly braces too
print(f"2 + 2 = {2 + 2}")          # 2 + 2 = 4
print(f"Upper: {subject.upper()}")  # Upper: WORLD

Stick with f-strings

f-strings (available since Python 3.6) are the modern standard. They are easier to read and faster to run than older approaches like % formatting or .format().

Operators

These symbols let you do maths and comparisons. The results are exactly what you would expect:

# Arithmetic
print(10 + 3)   # 13
print(10 - 3)   # 7
print(10 * 3)   # 30
print(10 / 3)   # 3.3333...  (always gives a decimal)
print(10 // 3)  # 3          (whole-number division, drops the remainder)
print(10 % 3)   # 1          (just the remainder)
print(2 ** 8)   # 256        (2 to the power of 8)

# Comparison (these give back True or False)
print(5 > 3)    # True
print(5 == 5)   # True
print(5 != 4)   # True

# Logical (combining True/False values)
print(True and False)  # False
print(True or False)   # True
print(not True)        # False

Control Flow

Control flow is how you tell Python to make decisions or repeat steps.

if / elif / else

This block checks a condition and runs different code depending on whether it is true. Think of it as an "if this, do that, otherwise do something else" instruction:

temperature = 72

if temperature > 90:
    print("Hot day")
elif temperature > 60:
    print("Nice day")
else:
    print("Cold day")
# Nice day

for loops

A for loop repeats a block of code once for each item in a collection. Think of it as "for each item in my list, do this":

chunks = ["chunk_1", "chunk_2", "chunk_3"]

for chunk in chunks:
    print(f"Processing: {chunk}")

# You can also loop over a range of numbers
for i in range(3):
    print(i)   # 0, 1, 2

while loops

A while loop keeps repeating as long as a condition is true. It stops as soon as the condition becomes false:

count = 0
while count < 3:
    print(f"Count: {count}")
    count += 1

Indentation is not decoration — it is the code

Python uses indentation (4 spaces) to show what is inside a block. There are no curly braces like in some other languages. If your indentation is inconsistent, Python will stop and tell you about it with a SyntaxError. Most editors handle this for you automatically.

Truthiness

Python has a neat shortcut: many values can act as True or False even when they are not booleans (the programming word for this is truthiness). These values are treated as False:

bool(0)       # False  (the number zero)
bool(0.0)     # False  (zero as a decimal)
bool("")      # False  (an empty string)
bool([])      # False  (an empty list)
bool(None)    # False  (the "nothing" value)

# Everything else is treated as True
bool(1)       # True
bool("hi")    # True
bool([0])     # True  (a list with something in it)

This lets you write clean, readable checks like this one:

text = ""
if not text:
    print("No text provided!")

Input and Print

print() sends text to your terminal. input() asks the user to type something:

# Print with custom separator and ending
print("Hello", "World", sep=", ", end="!\n")  # Hello, World!

# Ask the user to type something (always comes back as a string)
name = input("Enter your name: ")
print(f"Hi, {name}!")

You will rarely use input() in RAG projects

In scripts and data pipelines, you normally get your configuration from files or environment variables rather than typing it in. Do not worry if you never use input() — it is good to know it exists.

Try it yourself

Open the Python REPL (python in your terminal) and type these lines one at a time. Watch what comes back after each one. Try changing the numbers and strings to see what changes in the output.

x = 10
y = 3
print(f"{x} divided by {y} is {x / y:.2f}")

The :.2f inside the curly braces is a format hint that rounds the decimal to two places. You will see 10 divided by 3 is 3.33.

Next steps