1. Core Syntax & Basic Types

Python Cheat Sheets Quick Reference

Variables & Type Assignment


main.pyRunnable
## Dynamically-typed assignments
integer_val = 42
float_val = 3.14159
string_val = "Technical Reference"
boolean_val = True
null_val = None

## Multiple assignments
x, y, z = 1, 2, 3
x = y = z = 0  # Reassign all variables to a single reference

Basic Type Casts & Conversions


main.pyRunnable
int_cast = int("100")          # Returns 100
float_cast = float("3.14")      # Returns 3.14
str_cast = str(1024)           # Returns "1024"
bool_cast_empty = bool([])     # Returns False (empty containers are falsy)
bool_cast_filled = bool([0])   # Returns True (non-empty containers are truthy)

2. Collections & Data Structures

Lists (Mutable Sequences)

Time Complexities: Access $O(1)$ , Append $O(1)$ , Insert $O(n)$ , Delete $O(n)$ , Search $O(n)$ .


main.pyRunnable
items = [1, 2, 3]
items.append(4)               # Append to end: [1, 2, 3, 4]
items.insert(0, 99)           # Insert at index 0: [99, 1, 2, 3, 4]
items.remove(2)               # Remove first occurrence of value 2
popped_val = items.pop()      # Pop from end, returns popped value
items.sort()                  # Sort in-place
cloned_list = items[:]        # Shallow copy slice syntax

Dictionaries (Hash Maps)

Time Complexities: Get/Set $O(1)$ average, Delete $O(1)$ average.


main.pyRunnable
lookup = {"SKU-1": 10.50, "SKU-2": 24.99}
lookup["SKU-3"] = 5.00        # Insert key-value pair
val = lookup.get("SKU-9", 0.0) # Safe access with default fallback
del lookup["SKU-1"]           # Delete key

## Dictionary iterations
for key in lookup:
    pass # Iterate keys
for key, value in lookup.items():
    pass # Iterate key-value pairs

Sets (Unique Unordered Collections)

Time Complexities: Add/Remove/Membership $O(1)$ average.


main.pyRunnable
unique_skus = {"SKU-1", "SKU-2"}
unique_skus.add("SKU-3")
unique_skus.remove("SKU-1")

## Set operations
set_a = {1, 2, 3}
set_b = {3, 4, 5}
union_set = set_a | set_b        # {1, 2, 3, 4, 5}
intersect_set = set_a & set_b    # {3}
difference_set = set_a - set_b   # {1, 2}

Tuples (Immutable Sequences)

Time Complexities: Access $O(1)$ .


main.pyRunnable
record = ("CPU-9", 150.00, 10)
sku, cost, quantity = record  # Unpacking syntax
single_element_tuple = (42,)   # Requires trailing comma

3. Control Structures & Comprehensions

Conditional Branches


main.pyRunnable
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
else:
    grade = "C"

## Ternary assignment
result = "Pass" if score >= 60 else "Fail"

Iteration Loops


main.pyRunnable
## For loop with range bounds
for i in range(0, 10, 2):  # start, stop, step (0, 2, 4, 6, 8)
    pass

## Iterating index and value concurrently
for idx, item in enumerate(["A", "B", "C"]):
    pass

## Iterating multiple sequences simultaneously
for name, price in zip(["Screen", "Lens"], [150.0, 50.0]):
    pass

## While loop with conditional escape
count = 0
while count < 5:
    if count == 3:
        break
    count += 1
else:
    # Executes only if loop completes without hitting a 'break'
    pass

Comprehensions & Generators


main.pyRunnable
## List comprehension
squared_evens = [x**2 for x in range(10) if x % 2 == 0]

## Dict comprehension
sku_lookup = {f"SKU-{x}": x * 10 for x in range(3)}

## Set comprehension
unique_lengths = {len(w) for w in ["apple", "grape", "orange"]}

## Generator expression (memory optimized)
lazy_squares = (x**2 for x in range(1000000))

4. Functions & Lambda Operations

Function Parameters & Scopes


main.pyRunnable
def process_data(required_arg, default_arg="standard", *args, **kwargs):
    """
    *args: captures additional positional arguments as a tuple.
    **kwargs: captures additional keyword arguments as a dictionary.
    """
    return required_arg, default_arg, args, kwargs

## Global vs. Local scopes
value = 100

def modify_scope():
    global value
    value = 200  # Modifies global variable

Lambda Functions


main.pyRunnable
## Inline anonymous functions
add_numbers = lambda a, b: a + b
result = add_numbers(10, 5)  # 15

## Sorting collections using lambda key functions
items = [("Part-A", 15.0), ("Part-B", 5.0)]
items.sort(key=lambda x: x[1])  # Sorts ascending by price

5. String Manipulation

Formatting & Slicing


main.pyRunnable
## F-string interpolation
sku = "MCU-101"
price = 5.75
formatted = f"Item: {sku:<10} | Price: ${price:.2f}"

## String Slicing [start:stop:step]
text = "PythonFoundations"
substring = text[0:6]        # "Python"
reversed_text = text[::-1]    # "snoitadnuoFnohtyP"
last_two = text[-2:]         # "ns"

Core String Methods


main.pyRunnable
raw = "  isolated, data, block  "
clean = raw.strip()                   # Remove leading/trailing spaces
tokens = clean.split(", ")            # ["isolated", "data", "block"]
rebuilt = " - ".join(tokens)          # "isolated - data - block"
replaced = clean.replace("data", "x") # "isolated, x, block"
has_suffix = clean.endswith("block")   # True
is_digit_string = "12345".isdigit()   # True

6. File I/O & Exception Operations

Path Manipulation (`pathlib`)


main.pyRunnable
from pathlib import Path

## Path resolutions
directory_path = Path("public/courses")
file_path = directory_path / "metadata.json"  # Overloaded division operator

if file_path.is_file():
    print(f"File exists. Size: {file_path.stat().st_size} bytes.")

Stream Operations & Context Managers


main.pyRunnable
## Writing to a text file
with open("output.txt", "w", encoding="utf-8") as stream:
    stream.write("First line of record.\n")
    stream.write("Second line of record.\n")

## Reading from a text file
with open("output.txt", "r", encoding="utf-8") as stream:
    file_contents = stream.read()  # Loads entire file
    
## Streaming line-by-line (memory safe)
with open("output.txt", "r", encoding="utf-8") as stream:
    for line in stream:
        process_line = line.strip()

Exception Safety Blocks (EAFP)


main.pyRunnable
try:
    with open("vault.json", "r") as stream:
        data = stream.read()
except FileNotFoundError as error:
    print(f"Error: File missing. Details: {error}")
except OSError as error:
    print(f"System I/O Failure: {error}")
finally:
    print("Completed execution transaction.")

7. Pure Python Standard Libraries Reference

JSON Serialization (`json`)


main.pyRunnable
import json

## Encoding dictionary to string
payload = {"sku": "MCU-1", "cost": 1.50}
json_string = json.dumps(payload, indent=4)

## Decoding string to dictionary
decoded_dict = json.loads(json_string)

## Reading/Writing JSON file streams
with open("database.json", "w") as f:
    json.dump(payload, f, indent=4)

with open("database.json", "r") as f:
    data = json.load(f)

Logging Framework (`logging`)


main.pyRunnable
import logging

## Setup basic configuration logger
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] %(message)s"
)

logging.debug("Diagnostic telemetry - excluded unless log level is DEBUG.")
logging.info("Informational event record.")
logging.warning("Non-fatal anomalies detected.")
logging.error("Fatal transaction failures.")

Copy Operations (`copy`)


main.pyRunnable
import copy

original_nested = [[1, 2], [3, 4]]
shallow_clone = copy.copy(original_nested)     # Sub-lists references are shared
deep_clone = copy.deepcopy(original_nested)    # Copies both container and sub-elements

8. Common Patterns & Idioms

EAFP vs. LBYL

EAFP: Easier to Ask for Forgiveness than Permission. Python's standard programming paradigm.


main.pyRunnable
## Recommended (EAFP)
try:
    val = dict_data["key"]
except KeyError:
    val = "default"

## Avoid (LBYL - Look Before You Leap)
if "key" in dict_data:
    val = dict_data["key"]
else:
    val = "default"

Properties Decorators (Getter/Setter)


main.pyRunnable
class TemperatureSensor:
    def __init__(self, celsius: float):
        self._celsius = celsius

    @property
    def celsius(self) -> float:
        return self._celsius

    @celsius.setter
    def celsius(self, value: float):
        if value < -273.15:
            raise ValueError("Temperature below absolute zero is physically impossible.")
        self._celsius = value

9. Error Resolution Guide

Exception Name	Common Root Causes	Example Resolution Actions
`SyntaxError`	Invalid syntax structure (missing colons, unclosed brackets).	Check line formatting details and bracket nesting.
`IndentationError`	Inconsistent indentation sizes or mixed tabs and spaces.	Standardize all code layers to 4 spaces indent patterns.
`NameError`	Accessing an undefined identifier or variable.	Check identifier spelling and local scope bounds.
`TypeError`	Invoking operations on incompatible data types (e.g. `int + str`).	Apply explicit type casts (e.g. `str()` or `int()`).
`ValueError`	Parameter holds correct type but invalid values (e.g. `int("abc")`).	Wrap input processing inside robust validation loops.
`IndexError`	Attempting to access an index beyond sequence boundaries.	Verify sequence size utilizing `len()` beforehand.
`KeyError`	Accessing a non-existent dictionary key.	Use `dict.get(key, default)` for safe lookup operations.
`FileNotFoundError`	Attempting to open a missing file path.	Validate path structures using `path.is_file()` or path checks.

Reference Readiness Check

Self-Check: I can use properties to protect variables. (Click to check)
Self-Check: I can handle standard system exceptions safely using EAFP blocks. (Click to check)

Finished this lesson?

Mark it complete to advance your curriculum progress.

23 / 23

Python Cheat Sheets Quick Reference

1. Core Syntax & Basic Types

Variables & Type Assignment


main.pyRunnable
## Dynamically-typed assignments
integer_val = 42
float_val = 3.14159
string_val = "Technical Reference"
boolean_val = True
null_val = None

## Multiple assignments
x, y, z = 1, 2, 3
x = y = z = 0  # Reassign all variables to a single reference

Basic Type Casts & Conversions


main.pyRunnable
int_cast = int("100")          # Returns 100
float_cast = float("3.14")      # Returns 3.14
str_cast = str(1024)           # Returns "1024"
bool_cast_empty = bool([])     # Returns False (empty containers are falsy)
bool_cast_filled = bool([0])   # Returns True (non-empty containers are truthy)

2. Collections & Data Structures

Lists (Mutable Sequences)

Time Complexities: Access $O(1)$ , Append $O(1)$ , Insert $O(n)$ , Delete $O(n)$ , Search $O(n)$ .


main.pyRunnable
items = [1, 2, 3]
items.append(4)               # Append to end: [1, 2, 3, 4]
items.insert(0, 99)           # Insert at index 0: [99, 1, 2, 3, 4]
items.remove(2)               # Remove first occurrence of value 2
popped_val = items.pop()      # Pop from end, returns popped value
items.sort()                  # Sort in-place
cloned_list = items[:]        # Shallow copy slice syntax

Dictionaries (Hash Maps)

Time Complexities: Get/Set $O(1)$ average, Delete $O(1)$ average.


main.pyRunnable
lookup = {"SKU-1": 10.50, "SKU-2": 24.99}
lookup["SKU-3"] = 5.00        # Insert key-value pair
val = lookup.get("SKU-9", 0.0) # Safe access with default fallback
del lookup["SKU-1"]           # Delete key

## Dictionary iterations
for key in lookup:
    pass # Iterate keys
for key, value in lookup.items():
    pass # Iterate key-value pairs

Sets (Unique Unordered Collections)

Time Complexities: Add/Remove/Membership $O(1)$ average.


main.pyRunnable
unique_skus = {"SKU-1", "SKU-2"}
unique_skus.add("SKU-3")
unique_skus.remove("SKU-1")

## Set operations
set_a = {1, 2, 3}
set_b = {3, 4, 5}
union_set = set_a | set_b        # {1, 2, 3, 4, 5}
intersect_set = set_a & set_b    # {3}
difference_set = set_a - set_b   # {1, 2}

Tuples (Immutable Sequences)

Time Complexities: Access $O(1)$ .


main.pyRunnable
record = ("CPU-9", 150.00, 10)
sku, cost, quantity = record  # Unpacking syntax
single_element_tuple = (42,)   # Requires trailing comma

3. Control Structures & Comprehensions

Conditional Branches


main.pyRunnable
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
else:
    grade = "C"

## Ternary assignment
result = "Pass" if score >= 60 else "Fail"

Iteration Loops


main.pyRunnable
## For loop with range bounds
for i in range(0, 10, 2):  # start, stop, step (0, 2, 4, 6, 8)
    pass

## Iterating index and value concurrently
for idx, item in enumerate(["A", "B", "C"]):
    pass

## Iterating multiple sequences simultaneously
for name, price in zip(["Screen", "Lens"], [150.0, 50.0]):
    pass

## While loop with conditional escape
count = 0
while count < 5:
    if count == 3:
        break
    count += 1
else:
    # Executes only if loop completes without hitting a 'break'
    pass

Comprehensions & Generators


main.pyRunnable
## List comprehension
squared_evens = [x**2 for x in range(10) if x % 2 == 0]

## Dict comprehension
sku_lookup = {f"SKU-{x}": x * 10 for x in range(3)}

## Set comprehension
unique_lengths = {len(w) for w in ["apple", "grape", "orange"]}

## Generator expression (memory optimized)
lazy_squares = (x**2 for x in range(1000000))

4. Functions & Lambda Operations

Function Parameters & Scopes


main.pyRunnable
def process_data(required_arg, default_arg="standard", *args, **kwargs):
    """
    *args: captures additional positional arguments as a tuple.
    **kwargs: captures additional keyword arguments as a dictionary.
    """
    return required_arg, default_arg, args, kwargs

## Global vs. Local scopes
value = 100

def modify_scope():
    global value
    value = 200  # Modifies global variable

Lambda Functions


main.pyRunnable
## Inline anonymous functions
add_numbers = lambda a, b: a + b
result = add_numbers(10, 5)  # 15

## Sorting collections using lambda key functions
items = [("Part-A", 15.0), ("Part-B", 5.0)]
items.sort(key=lambda x: x[1])  # Sorts ascending by price

5. String Manipulation

Formatting & Slicing


main.pyRunnable
## F-string interpolation
sku = "MCU-101"
price = 5.75
formatted = f"Item: {sku:<10} | Price: ${price:.2f}"

## String Slicing [start:stop:step]
text = "PythonFoundations"
substring = text[0:6]        # "Python"
reversed_text = text[::-1]    # "snoitadnuoFnohtyP"
last_two = text[-2:]         # "ns"

Core String Methods


main.pyRunnable
raw = "  isolated, data, block  "
clean = raw.strip()                   # Remove leading/trailing spaces
tokens = clean.split(", ")            # ["isolated", "data", "block"]
rebuilt = " - ".join(tokens)          # "isolated - data - block"
replaced = clean.replace("data", "x") # "isolated, x, block"
has_suffix = clean.endswith("block")   # True
is_digit_string = "12345".isdigit()   # True

6. File I/O & Exception Operations

Path Manipulation (`pathlib`)


main.pyRunnable
from pathlib import Path

## Path resolutions
directory_path = Path("public/courses")
file_path = directory_path / "metadata.json"  # Overloaded division operator

if file_path.is_file():
    print(f"File exists. Size: {file_path.stat().st_size} bytes.")

Stream Operations & Context Managers


main.pyRunnable
## Writing to a text file
with open("output.txt", "w", encoding="utf-8") as stream:
    stream.write("First line of record.\n")
    stream.write("Second line of record.\n")

## Reading from a text file
with open("output.txt", "r", encoding="utf-8") as stream:
    file_contents = stream.read()  # Loads entire file
    
## Streaming line-by-line (memory safe)
with open("output.txt", "r", encoding="utf-8") as stream:
    for line in stream:
        process_line = line.strip()

Exception Safety Blocks (EAFP)


main.pyRunnable
try:
    with open("vault.json", "r") as stream:
        data = stream.read()
except FileNotFoundError as error:
    print(f"Error: File missing. Details: {error}")
except OSError as error:
    print(f"System I/O Failure: {error}")
finally:
    print("Completed execution transaction.")

7. Pure Python Standard Libraries Reference

JSON Serialization (`json`)


main.pyRunnable
import json

## Encoding dictionary to string
payload = {"sku": "MCU-1", "cost": 1.50}
json_string = json.dumps(payload, indent=4)

## Decoding string to dictionary
decoded_dict = json.loads(json_string)

## Reading/Writing JSON file streams
with open("database.json", "w") as f:
    json.dump(payload, f, indent=4)

with open("database.json", "r") as f:
    data = json.load(f)

Logging Framework (`logging`)


main.pyRunnable
import logging

## Setup basic configuration logger
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] %(message)s"
)

logging.debug("Diagnostic telemetry - excluded unless log level is DEBUG.")
logging.info("Informational event record.")
logging.warning("Non-fatal anomalies detected.")
logging.error("Fatal transaction failures.")

Copy Operations (`copy`)


main.pyRunnable
import copy

original_nested = [[1, 2], [3, 4]]
shallow_clone = copy.copy(original_nested)     # Sub-lists references are shared
deep_clone = copy.deepcopy(original_nested)    # Copies both container and sub-elements

8. Common Patterns & Idioms

EAFP vs. LBYL

EAFP: Easier to Ask for Forgiveness than Permission. Python's standard programming paradigm.


main.pyRunnable
## Recommended (EAFP)
try:
    val = dict_data["key"]
except KeyError:
    val = "default"

## Avoid (LBYL - Look Before You Leap)
if "key" in dict_data:
    val = dict_data["key"]
else:
    val = "default"

Properties Decorators (Getter/Setter)


main.pyRunnable
class TemperatureSensor:
    def __init__(self, celsius: float):
        self._celsius = celsius

    @property
    def celsius(self) -> float:
        return self._celsius

    @celsius.setter
    def celsius(self, value: float):
        if value < -273.15:
            raise ValueError("Temperature below absolute zero is physically impossible.")
        self._celsius = value

9. Error Resolution Guide

Exception Name	Common Root Causes	Example Resolution Actions
`SyntaxError`	Invalid syntax structure (missing colons, unclosed brackets).	Check line formatting details and bracket nesting.
`IndentationError`	Inconsistent indentation sizes or mixed tabs and spaces.	Standardize all code layers to 4 spaces indent patterns.
`NameError`	Accessing an undefined identifier or variable.	Check identifier spelling and local scope bounds.
`TypeError`	Invoking operations on incompatible data types (e.g. `int + str`).	Apply explicit type casts (e.g. `str()` or `int()`).
`ValueError`	Parameter holds correct type but invalid values (e.g. `int("abc")`).	Wrap input processing inside robust validation loops.
`IndexError`	Attempting to access an index beyond sequence boundaries.	Verify sequence size utilizing `len()` beforehand.
`KeyError`	Accessing a non-existent dictionary key.	Use `dict.get(key, default)` for safe lookup operations.
`FileNotFoundError`	Attempting to open a missing file path.	Validate path structures using `path.is_file()` or path checks.

Reference Readiness Check

Self-Check: I can use properties to protect variables. (Click to check)
Self-Check: I can handle standard system exceptions safely using EAFP blocks. (Click to check)

Finished this lesson?

Mark it complete to advance your curriculum progress.

23 / 23

Python Foundations

Python Cheat Sheets Quick Reference

1. Core Syntax & Basic Types

Variables & Type Assignment

Basic Type Casts & Conversions

2. Collections & Data Structures

Lists (Mutable Sequences)

Dictionaries (Hash Maps)

Sets (Unique Unordered Collections)

Tuples (Immutable Sequences)

3. Control Structures & Comprehensions

Conditional Branches

Iteration Loops

Comprehensions & Generators

4. Functions & Lambda Operations

Function Parameters & Scopes

Lambda Functions

5. String Manipulation

Formatting & Slicing

Core String Methods

6. File I/O & Exception Operations

Path Manipulation (pathlib)

Stream Operations & Context Managers

Exception Safety Blocks (EAFP)

7. Pure Python Standard Libraries Reference

JSON Serialization (json)

Logging Framework (logging)

Copy Operations (copy)

8. Common Patterns & Idioms

EAFP vs. LBYL

Properties Decorators (Getter/Setter)

9. Error Resolution Guide

Reference Readiness Check

Finished this lesson?

Python Foundations

Python Cheat Sheets Quick Reference

1. Core Syntax & Basic Types

Variables & Type Assignment

Basic Type Casts & Conversions

2. Collections & Data Structures

Lists (Mutable Sequences)

Dictionaries (Hash Maps)

Sets (Unique Unordered Collections)

Tuples (Immutable Sequences)

3. Control Structures & Comprehensions

Conditional Branches

Iteration Loops

Comprehensions & Generators

4. Functions & Lambda Operations

Function Parameters & Scopes

Lambda Functions

5. String Manipulation

Formatting & Slicing

Core String Methods

6. File I/O & Exception Operations

Path Manipulation (pathlib)

Stream Operations & Context Managers

Exception Safety Blocks (EAFP)

7. Pure Python Standard Libraries Reference

JSON Serialization (json)

Logging Framework (logging)

Copy Operations (copy)

8. Common Patterns & Idioms

EAFP vs. LBYL

Properties Decorators (Getter/Setter)

9. Error Resolution Guide

Reference Readiness Check

Finished this lesson?

Path Manipulation (`pathlib`)

JSON Serialization (`json`)

Logging Framework (`logging`)

Copy Operations (`copy`)

Path Manipulation (`pathlib`)

JSON Serialization (`json`)

Logging Framework (`logging`)

Copy Operations (`copy`)