error handeling doc

Docs/Basic/07-error-handeling.md

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+# 06 – Error Handling, Linting, Formatting, and Testing in Python
+
+This document explains how Python handles runtime errors, how to write safer code using `try / except`, and how to improve code quality using **linting**, **formatting**, and **unit testing** tools.
+
+---
+
+## 1. Error Handling with `try / except`
+
+Python uses `try / except` blocks to handle runtime errors gracefully without crashing the program.
+
+### Example
+
+```python
+def abbas(a, b):
+    try:
+        res = a / b
+        print(res)
+    except ZeroDivisionError:
+        print("Zero Number Detected")
+    except Exception as e:
+        print(f"Error Detected {e}")
+
+abbas(1, 0)
+```
+
+### Explanation
+
+* The code inside `try` is executed first.
+* If no error occurs, the result is printed.
+* If `b` is `0`, a `ZeroDivisionError` is raised.
+* The specific `ZeroDivisionError` block runs first.
+* Any other error is caught by the generic `Exception` block.
+
+### Key Rule
+
+* Always catch **specific exceptions first**.
+* Use `Exception` only as a fallback.
+
+---
+
+## 2. Full `try / except` Structure
+
+Python supports additional blocks for more control.
+
+### Syntax
+
+```python
+try:
+    # code that may raise an error
+except:
+    # runs if an error occurs
+else:
+    # runs if no error occurs
+finally:
+    # always runs
+```
+
+### Explanation
+
+* `try`: code that may fail
+* `except`: handles errors
+* `else`: runs only if no exception occurred
+* `finally`: runs no matter what (used for cleanup)
+
+---
+
+## 3. Linting with `pylint`
+
+Linting analyzes code for:
+
+* Syntax errors
+* Style problems
+* Bad practices
+
+### Basic Command
+
+```bash
+pylint main.py
+```
+
+### Detailed Report
+
+```bash
+pylint --report y main.py
+```
+
+### Explanation
+
+* `pylint` gives a score and suggestions.
+* Helps maintain readable and maintainable code.
+* Commonly used in professional Python projects.
+
+---
+
+## 4. Code Formatting with `black`
+
+`black` is an automatic code formatter that enforces a consistent style.
+
+### Command
+
+```bash
+black main.py
+```
+
+### Explanation
+
+* Reformats code automatically.
+* Removes style debates.
+* Safe and widely used.
+
+---
+
+## 5. Unit Testing with `unittest`
+
+Unit tests verify that individual parts of code behave as expected.
+
+---
+
+### Application Code
+
+#### `abbas.py`
+
+```python
+def bemola(a, b):
+    try:
+        res = a / b
+        print(res)
+    except ZeroDivisionError:
+        print("Zero Number Detected")
+    except Exception as e:
+        print(f"Error Detected {e}")
+```
+
+---
+
+### Test Code
+
+#### `abbas_test.py`
+
+```python
+import unittest
+from abbas import bemola
+
+class TestAbbas(unittest.TestCase):
+
+    def test_bemola(self):
+        a = 10
+        b = 2
+        self.assertEqual(bemola(a, b), 5)
+
+if __name__ == "__main__":
+    unittest.main()
+```
+
+---
+
+### Explanation
+
+#### `unittest.TestCase`
+
+* Base class for writing test cases.
+
+#### Test Method
+
+```python
+def test_bemola(self):
+```
+
+* Test methods must start with `test_`.
+
+#### Assertion
+
+```python
+self.assertEqual(bemola(a, b), 5)
+```
+
+* Checks if the function returns the expected result.
+
+---
+
+### Important Note (Design Issue)
+
+The function `bemola` **prints** the result but does not return it.
+
+```python
+print(res)
+```
+
+This causes the test to fail because the function returns `None`.
+
+#### Correct Implementation
+
+```python
+def bemola(a, b):
+    try:
+        return a / b
+    except ZeroDivisionError:
+        return "Zero Number Detected"
+    except Exception as e:
+        return f"Error Detected {e}"
+```
+
+This version:
+
+* Returns values instead of printing
+* Is testable
+* Follows best practices
+
+---
+
+## Summary
+
+* `try / except` prevents program crashes
+* `else` runs only when no error occurs
+* `finally` always runs
+* `pylint` improves code quality
+* `black` enforces formatting
+* `unittest` verifies correctness
+* Functions should **return values**, not print them, when tested