Module 04: Intermediate Python

🎯 Learning Objectives

• Handle exceptions gracefully
• Work with files and paths
• Use regular expressions for pattern matching
• Manipulate dates and times
• Apply object-oriented programming

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📋 CHEATSHEET: Exception Handling

┌─────────────────────────────────────────────────────────────────────┐
│                     EXCEPTION HANDLING                              │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│  try:                                                               │
│      risky_operation()                                              │
│  except ValueError as e:          # Specific exception             │
│      handle_value_error(e)                                          │
│  except (TypeError, KeyError):    # Multiple exceptions            │
│      handle_type_or_key()                                           │
│  except Exception as e:           # Catch-all (use sparingly)      │
│      log_error(e)                                                   │
│      raise                        # Re-raise                        │
│  else:                            # No exception occurred           │
│      success_action()                                               │
│  finally:                         # Always runs                     │
│      cleanup()                                                      │
│                                                                     │
│  COMMON EXCEPTIONS                                                  │
│  ─────────────────                                                  │
│  ValueError    - Invalid value         KeyError    - Dict key miss │
│  TypeError     - Wrong type            IndexError  - List index    │
│  FileNotFoundError - No file           AttributeError - No attr    │
│                                                                     │
└─────────────────────────────────────────────────────────────────────┘

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📋 CHEATSHEET: File Handling

# Read file
with open('file.txt', 'r') as f:
    content = f.read()          # All at once
    lines = f.readlines()       # List of lines
    for line in f:              # Memory efficient
        process(line)

# Write file
with open('file.txt', 'w') as f:
    f.write("Hello\n")
    f.writelines(["line1\n", "line2\n"])

# Path operations (pathlib)
from pathlib import Path
path = Path('/data/file.csv')
path.exists()       # True/False
path.name           # 'file.csv'
path.stem           # 'file'
path.suffix         # '.csv'
path.parent         # Path('/data')
list(path.parent.glob('*.csv'))  # All CSVs in dir

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📋 CHEATSHEET: Regular Expressions

import re

# Common patterns
r'\d+'        # One or more digits
r'\w+'        # Word characters
r'\s+'        # Whitespace
r'^start'     # Start of string
r'end$'       # End of string
r'[a-zA-Z]+'  # Letters only

# Methods
re.search(pattern, text)    # Find first match
re.findall(pattern, text)   # Find all matches
re.sub(pattern, repl, text) # Replace
re.split(pattern, text)     # Split on pattern

# Examples
emails = re.findall(r'\S+@\S+', text)
cleaned = re.sub(r'\s+', ' ', text)
parts = re.split(r'[,;]\s*', text)

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📋 CHEATSHEET: Datetime

from datetime import datetime, date, timedelta

# Current
now = datetime.now()
today = date.today()

# Parse/format
dt = datetime.strptime("2024-03-15", "%Y-%m-%d")
s = dt.strftime("%B %d, %Y")  # "March 15, 2024"

# Arithmetic
tomorrow = today + timedelta(days=1)
diff = date1 - date2  # timedelta

# Components
dt.year, dt.month, dt.day
dt.hour, dt.minute, dt.second
dt.weekday()  # 0=Monday

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📋 CHEATSHEET: OOP

class DataProcessor:
    """Process data records."""
    
    default_batch = 1000          # Class attribute
    
    def __init__(self, name):
        self.name = name          # Instance attribute
        
    def process(self, records):
        """Instance method."""
        return [self._transform(r) for r in records]
    
    def _transform(self, record):  # Private method
        return record
    
    @property
    def info(self):               # Property
        return f"Processor: {self.name}"
    
    @classmethod
    def create(cls, name):        # Class method
        return cls(name)
    
    @staticmethod
    def validate(record):         # Static method
        return 'id' in record

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🎓 Key Takeaways

1. Always use with for files - Ensures proper cleanup
2. Catch specific exceptions - Avoid bare except:
3. Use pathlib over os.path - More Pythonic
4. Compile regex for reuse - re.compile(pattern)
5. Prefer composition - Over deep inheritance

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📚 Navigation

← Back to Module 03: Functions & Modules

→ Continue to Module 05: Data Engineering Essentials