More Basics

1. Package Management (PIP)

pip installs Python packages from the Python Package Index (PyPI).

• Install: pip install <package_name>
• Specific Version: pip install <package_name>=='version_num'
• Minimum Version: pip install <package_name> >= 'version_num'
• Upgrade Package: pip install --upgrade <package_name>
• Upgrade Pip Itself: pip install -U pip
• Search: pip search "query"
• Snapshot Environment: pip freeze > requirements.txt (Lists packages case-insensitively).
• Restore Environment: pip install -r requirements.txt

2. Execution Environments & Tooling

• REPL (Interactive Console): Read-Eval-Print Loop. Start by typing python. Executes line-by-line instantly.
• Script Mode: Run full files via python script.py or ./script.py (Unix executable).
• IDEs/Editors: PyCharm, Eclipse+PyDev, Sublime Text, Vim. Python only requires a raw text editor, but IDEs provide PEP 8 checks and syntax highlighting.

3. Syntax Rules & Structure

• Identifiers (Variables/Functions/Classes): * Allowed: a-z, A-Z, 0-9, _.
  • Rules: Cannot start with a digit. Cannot be only digits. Cannot be a reserved Keyword. Case-sensitive (EPAM != Epam).
• Keywords: Built-in reserved words (e.g., False, def, if, return). Do not require importing.
• Quotes: * Single (' ') and double (" ") are identical in function.
  • Triple (""" """ or ''' ''') are used for multiline strings and docstrings.
  • Nest quotes by alternating types: "Here is 'text'"
• Indentation: * Python uses whitespace (standard is 4 spaces) instead of {} to define code blocks.
  • Inconsistent indentation throws an IndentationError.
• Multi-line Statements: * Manual break: Use the backslash \ at the end of a line.
  • Automatic break: Statements inside (), [], or {} wrap automatically without a \.
• Comments: Proceeded by the # symbol.

4. Variables & Dynamic Typing

Python is dynamically typed; you do not declare variable types explicitly. A variable is simply a reference pointing to an object in memory.

• Integers: Whole numbers. Unlimited length (bound only by system memory).
• Floats: Decimals.
• Strings: Text characters.
• Multiple Assignment: a, b, c = 1, 2, "john" or a = b = c = 1
• Deletion: del var_name removes the reference. Accessing it afterward throws a NameError.
• Type Conversion: int(x), float(x), str(x).

5. The Python Data Model: Immutable vs. Mutable

Every object possesses three core traits:

1. Identity: Memory address. Evaluated with is. Checked with id(). Unchangeable.
2. Type: Defines supported operations. Checked with type(). Unchangeable.
3. Value: The actual data.

Category	Definition	Common Data Types	Memory Logic
Immutable	The object’s value cannot be changed after creation. Any “modification” actually creates a new object in memory.	int, float, bool, str, tuple, frozenset	Changing the value results in a new object with a new id().
Mutable	The object’s value can be modified after creation without creating a new object.	list, dict, set, most custom objects	Modifying the object keeps the same id() because it changes in place.

Example

Immutable

x=10
print(id(x))

x=x+5
print(id(x))# Different id

Mutable

x= [1,2,3]
print(id(x))

x.append(4)
print(id(x))# Same id

6. Operators

• Arithmetic: +, -,* , / (float division), % (modulo/remainder), ** (exponent), // integer dividion
• Assignment: =, +=, =, etc.
• Comparison: ==, !=, >, <, >=, <=. Returns boolean True or False.
• Membership: in and not in (e.g., 'a' in 'apple' -> True).
• Identity: is and is not (Checks if two variables point to the exact same memory address. x == y tests value equivalence; x is y tests memory equivalence).

7. Control Flow & I/O

• Conditionals (if/elif/else): Top-down evaluation.
• Ternary Operator (One-line if): print("even" if a % 2 == 0 else "odd")
• Input/Output: * input("Prompt: ") strictly returns string data. Wrap in int() to parse numbers.
  • print(a, b) automatically converts arguments to strings and joins them with spaces.

8. PEP 8 (Python Enhancement Proposal 8)

• Purpose: The official style guide written in 2001 by Guido van Rossum to ensure code consistency and readability.
• Philosophy: “Code is read much more often than it is written.”
• Linters/Tools: pycodestyle, flake8 (Install via pip to automatically check scripts against PEP 8 rules).

Loops and Strings

List & Tuples

Set & Dict

Function & Input