Feat/architecture

architecture/strings/index.md

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+# Python Strings - Quick Reference
+
+## Table of Contents
+
+1. [String Basics](#basics)
+2. [String Methods](#methods)
+3. [String Formatting](#formatting)
+4. [Practical Examples](#practical)
+
+---
+
+## String Basics {#basics}
+
+### Creating Strings
+
+```python
+single = 'Hello'
+double = "World"
+triple = '''Multi
+line'''
+```
+
+### String Operations
+
+| Operation     | Example                   | Result          |
+| ------------- | ------------------------- | --------------- |
+| Concatenation | `"Hello" + " " + "World"` | `"Hello World"` |
+| Repetition    | `"Ha" * 3`                | `"HaHaHa"`      |
+| Length        | `len("Python")`           | `6`             |
+| Membership    | `"a" in "apple"`          | `True`          |
+
+### Indexing & Slicing
+
+```python
+text = "Python"
+
+# Indexing (0-based)
+text[0]    # 'P' (first)
+text[-1]   # 'n' (last)
+
+# Slicing [start:end:step]
+text[0:3]  # 'Pyt'
+text[2:]   # 'thon'
+text[:4]   # 'Pyth'
+text[::2]  # 'Pto' (every 2nd)
+text[::-1] # 'nohtyP' (reverse)
+```
+
+📁 [basics.py](file:///Users/ragul/Documents/PERSONAL/python-starter-kit/starter_kit/strings/basics.py)
+
+---
+
+## String Methods {#methods}
+
+### Case Conversion
+
+| Method         | Example                 | Result          |
+| -------------- | ----------------------- | --------------- |
+| `upper()`      | `"hello".upper()`       | `"HELLO"`       |
+| `lower()`      | `"HELLO".lower()`       | `"hello"`       |
+| `title()`      | `"hello world".title()` | `"Hello World"` |
+| `capitalize()` | `"hello".capitalize()`  | `"Hello"`       |
+| `swapcase()`   | `"Hello".swapcase()`    | `"hELLO"`       |
+
+### Whitespace
+
+| Method     | Example             | Result   |
+| ---------- | ------------------- | -------- |
+| `strip()`  | `"  hi  ".strip()`  | `"hi"`   |
+| `lstrip()` | `"  hi  ".lstrip()` | `"hi  "` |
+| `rstrip()` | `"  hi  ".rstrip()` | `"  hi"` |
+
+### Search & Replace
+
+| Method              | Description                                | Example                                 |
+| ------------------- | ------------------------------------------ | --------------------------------------- |
+| `find(sub)`         | Find substring (returns -1 if not found)   | `"hello".find("ll")` → `2`              |
+| `index(sub)`        | Find substring (raises error if not found) | `"hello".index("ll")` → `2`             |
+| `count(sub)`        | Count occurrences                          | `"hello".count("l")` → `2`              |
+| `startswith(sub)`   | Check if starts with                       | `"hello".startswith("he")` → `True`     |
+| `endswith(sub)`     | Check if ends with                         | `"hello".endswith("lo")` → `True`       |
+| `replace(old, new)` | Replace substring                          | `"hi".replace("i", "ello")` → `"hello"` |
+
+### Split & Join
+
+```python
+# Split
+"a,b,c".split(',')        # ['a', 'b', 'c']
+"hello world".split()     # ['hello', 'world']
+
+# Join
+"-".join(['a', 'b', 'c']) # 'a-b-c'
+" ".join(['hi', 'there']) # 'hi there'
+```
+
+### Validation
+
+| Method      | Checks if...   | Example                            |
+| ----------- | -------------- | ---------------------------------- |
+| `isalpha()` | All alphabetic | `"abc".isalpha()` → `True`         |
+| `isdigit()` | All digits     | `"123".isdigit()` → `True`         |
+| `isalnum()` | Alphanumeric   | `"abc123".isalnum()` → `True`      |
+| `isspace()` | All whitespace | `"   ".isspace()` → `True`         |
+| `isupper()` | All uppercase  | `"ABC".isupper()` → `True`         |
+| `islower()` | All lowercase  | `"abc".islower()` → `True`         |
+| `istitle()` | Title case     | `"Hello World".istitle()` → `True` |
+
+📁 [methods.py](file:///Users/ragul/Documents/PERSONAL/python-starter-kit/starter_kit/strings/methods.py)
+
+---
+
+## String Formatting {#formatting}
+
+### 1. F-Strings (Recommended) ⭐
+
+```python
+name = "Ragul"
+age = 25
+price = 99.99
+
+# Basic
+f"Hello, {name}!"                    # "Hello, Ragul!"
+f"{name} is {age} years old"         # "Ragul is 25 years old"
+
+# Expressions
+f"10 + 5 = {10 + 5}"                 # "10 + 5 = 15"
+
+# Formatting
+f"Price: ₹{price:.2f}"               # "Price: ₹99.99"
+f"{1234567:,}"                       # "1,234,567"
+f"{0.85:.1%}"                        # "85.0%"
+
+# Alignment
+f"{'left':<10}"                      # "left      "
+f"{'right':>10}"                     # "     right"
+f"{'center':^10}"                    # "  center  "
+
+# Padding
+f"{42:05d}"                          # "00042"
+```
+
+### 2. format() Method
+
+```python
+"Hello, {}!".format(name)                      # Positional
+"{1} is {0}".format(age, name)                 # By position
+"{n} is {a}".format(n=name, a=age)            # Named
+"Price: ₹{:.2f}".format(price)                # Formatting
+```
+
+### 3. % Formatting (Old Style)
+
+```python
+"Hello, %s!" % name                  # String
+"%s is %d years old" % (name, age)   # Multiple
+"Price: ₹%.2f" % price               # Float
+```
+
+### Format Specifiers
+
+| Specifier | Meaning               | Example                          |
+| --------- | --------------------- | -------------------------------- |
+| `:d`      | Integer               | `f"{42:d}"` → `"42"`             |
+| `:f`      | Float                 | `f"{3.14:f}"` → `"3.140000"`     |
+| `:.2f`    | 2 decimal places      | `f"{3.14159:.2f}"` → `"3.14"`    |
+| `:,`      | Comma separator       | `f"{1000:,}"` → `"1,000"`        |
+| `:%`      | Percentage            | `f"{0.5:%}"` → `"50.000000%"`    |
+| `:<10`    | Left align (width 10) | `f"{'hi':<10}"` → `"hi        "` |
+| `:>10`    | Right align           | `f"{'hi':>10}"` → `"        hi"` |
+| `:^10`    | Center align          | `f"{'hi':^10}"` → `"    hi    "` |
+| `:05d`    | Zero padding          | `f"{42:05d}"` → `"00042"`        |
+
+📁 [formatting.py](file:///Users/ragul/Documents/PERSONAL/python-starter-kit/starter_kit/strings/formatting.py)
+
+---
+
+## Practical Examples {#practical}
+
+### 1. Email Validation
+
+```python
+email = "user@example.com"
+if "@" in email and "." in email.split("@")[1]:
+    print("✅ Valid")
+```
+
+### 2. Password Strength
+
+```python
+password = "Secret@123"
+has_upper = any(c.isupper() for c in password)
+has_lower = any(c.islower() for c in password)
+has_digit = any(c.isdigit() for c in password)
+is_strong = all([has_upper, has_lower, has_digit, len(password) >= 8])
+```
+
+### 3. Name Formatting
+
+```python
+name = "  ragul PALANISAMY  "
+formatted = name.strip().title()  # "Ragul Palanisamy"
+```
+
+### 4. URL Slug
+
+```python
+title = "Python String Tutorial"
+slug = title.lower().replace(" ", "-")  # "python-string-tutorial"
+```
+
+### 5. Extract Domain
+
+```python
+email = "user@company.com"
+domain = email.split("@")[1]  # "company.com"
+```
+
+### 6. Reverse Words
+
+```python
+sentence = "Hello World"
+reversed = " ".join(sentence.split()[::-1])  # "World Hello"
+```
+
+### 7. Count Vowels
+
+```python
+text = "Hello World"
+vowels = "aeiouAEIOU"
+count = sum(1 for c in text if c in vowels)  # 3
+```
+
+### 8. Palindrome Check
+
+```python
+word = "radar"
+is_palindrome = word == word[::-1]  # True
+```
+
+### 9. Mask Credit Card
+
+```python
+card = "1234567890123456"
+masked = "*" * 12 + card[-4:]  # "************3456"
+```
+
+### 10. Remove Duplicates
+
+```python
+text = "programming"
+unique = "".join(dict.fromkeys(text))  # "progamin"
+```
+
+📁 [practical.py](file:///Users/ragul/Documents/PERSONAL/python-starter-kit/starter_kit/strings/practical.py)
+
+---
+
+## Quick Tips
+
+### ✅ Best Practices
+
+1. **Use f-strings** for formatting (Python 3.6+)
+2. **Use `.strip()`** to remove whitespace
+3. **Strings are immutable** - methods return new strings
+4. **Use `in`** for membership testing
+5. **Use `.join()`** for concatenating many strings
+
+### ⚠️ Common Mistakes
+
+```python
+# ❌ BAD - Modifying strings in loop
+result = ""
+for word in words:
+    result += word  # Creates new string each time
+
+# ✅ GOOD - Use join
+result = "".join(words)
+
+# ❌ BAD - Using + for many strings
+text = str1 + str2 + str3 + str4
+
+# ✅ GOOD - Use f-string or join
+text = f"{str1}{str2}{str3}{str4}"
+```
+
+---
+
+## Summary
+
+| Category   | Key Methods                     | Use Case                      |
+| ---------- | ------------------------------- | ----------------------------- |
+| **Case**   | `upper()`, `lower()`, `title()` | Formatting names, comparison  |
+| **Clean**  | `strip()`, `replace()`          | Remove whitespace, clean data |
+| **Search** | `find()`, `count()`, `in`       | Find substrings               |
+| **Split**  | `split()`, `join()`             | Parse CSV, build sentences    |
+| **Check**  | `isdigit()`, `isalpha()`        | Validate input                |
+| **Format** | f-strings, `format()`           | Display data                  |
+
+**Remember:**
+
+- Strings are **immutable** (cannot be changed)
+- Indexing starts at **0**
+- Negative indices count from the **end**
+- Use **f-strings** for modern formatting
+- Always **validate** user input