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+# 09 – Python Standard Library
+
+This document introduces some of the most commonly used **Python standard library** modules:
+
+* `datetime`
+* `math`
+* `random`
+* `decimal`
+
+These modules come bundled with Python and require no external installation.
+
+---
+
+## 1. Date and Time with `datetime`
+
+The `datetime` module provides classes for working with dates and times.
+
+---
+
+### Working with Dates
+
+#### Code
+
+```python
+import datetime
+
+date_1 = datetime.date(2026, 1, 1)
+
+print(date_1.year)
+print(date_1.month)
+print(date_1.day)
+
+print(date_1.weekday)
+print(date_1.ctime)
+```
+
+#### Explanation
+
+* `datetime.date(year, month, day)` creates a date object.
+* `.year`, `.month`, `.day` access individual components.
+
+#### Important Note
+
+```python
+date_1.weekday()
+```
+
+* Returns the day of the week as an integer:
+
+  * Monday = 0
+  * Sunday = 6
+
+```python
+date_1.ctime()
+```
+
+* Returns a human-readable string representation of the date.
+
+---
+
+### Working with Time
+
+#### Code
+
+```python
+time_1 = datetime.time(12, 12)
+
+print(time_1.hour)
+print(time_1.min)
+```
+
+#### Explanation
+
+* `datetime.time(hour, minute)` creates a time object.
+* `.hour` returns the hour.
+* `.minute` returns the minute.
+
+---
+
+### Working with Date and Time Together
+
+#### Code
+
+```python
+abbas_birth = datetime.datetime(2026, 1, 1, 12, 12)
+today = datetime.date.today()
+now = datetime.datetime.now()
+
+diff_time = now - abbas_birth
+```
+
+#### Explanation
+
+* `datetime.datetime` includes both date and time.
+* `date.today()` returns today’s date.
+* `datetime.now()` returns the current date and time.
+* Subtracting two `datetime` objects returns a `timedelta`.
+
+---
+
+## 2. Mathematical Operations with `math`
+
+The `math` module provides advanced mathematical functions and constants.
+
+---
+
+### Mathematical Constants
+
+```python
+import math
+
+print(math.pi)
+print(math.e)
+print(math.inf)
+```
+
+* `math.pi`: π constant
+* `math.e`: Euler’s number
+* `math.inf`: infinity
+
+---
+
+### Power and Rounding
+
+```python
+print(math.pow(2, 3))
+
+print(round(4.2))
+print(round(4.8))
+```
+
+* `math.pow(a, b)` returns `a` raised to the power of `b`.
+* `round()` rounds to the nearest integer.
+
+---
+
+### Floor and Ceil
+
+```python
+print(math.floor(4.2))
+print(math.floor(4.9))
+
+print(math.ceil(4.2))
+print(math.ceil(4.9))
+```
+
+* `floor`: rounds down
+* `ceil`: rounds up
+
+---
+
+### Logarithms
+
+```python
+print(math.log(100, 10))
+```
+
+* Returns the logarithm of 100 with base 10.
+
+---
+
+## 3. Random Values with `random`
+
+The `random` module is used to generate pseudo-random values.
+
+---
+
+### Random Numbers
+
+```python
+import random
+
+print(random.randint(1, 6))
+print(random.random())
+```
+
+* `randint(a, b)`: random integer between `a` and `b` (inclusive)
+* `random()`: random float between `0` and `1`
+
+---
+
+### Random Selection
+
+```python
+number_list = list(range(15))
+print(random.choice(number_list))
+
+char_list = ['a', 'm', 's']
+print(random.choice(char_list))
+```
+
+* `choice()` selects a random element from a sequence.
+
+---
+
+### Shuffling
+
+```python
+random.shuffle(number_list)
+print(number_list)
+```
+
+* `shuffle()` randomly rearranges the list in place.
+
+---
+
+## 4. Decimal Precision with `decimal`
+
+The `decimal` module provides precise decimal arithmetic, avoiding floating-point errors.
+
+---
+
+### Decimal Context
+
+```python
+import decimal
+
+print(decimal.getcontext())
+```
+
+* Shows current precision and rounding settings.
+
+---
+
+### Float vs Decimal
+
+```python
+print(decimal.Decimal(0.1))
+print(decimal.Decimal('0.1'))
+```
+
+* Passing a float carries floating-point error.
+* Passing a string preserves exact value.
+
+---
+
+### Precision Comparison
+
+```python
+print(0.1 + 0.2 == 0.3)
+```
+
+Returns `False` due to floating-point precision issues.
+
+```python
+print(decimal.Decimal(0.1) + decimal.Decimal(0.2) == decimal.Decimal(0.3))
+```
+
+Still `False` because the floats are imprecise.
+
+```python
+print(decimal.Decimal('0.1') + decimal.Decimal('0.2') == decimal.Decimal('0.3'))
+```
+
+Returns `True` because strings preserve precision.
+
+---
+
+## Summary
+
+* `datetime` handles dates and times
+* `math` provides mathematical constants and functions
+* `random` generates pseudo-random values
+* `decimal` solves floating-point precision problems
+* Always use strings when creating `Decimal` values
+