Why My Code Works Locally but Fails on Submission (Common Reasons)

# ❌ Absolute path - only works on your computer
file_path = "C:/Users/John/Documents/data.txt"

# ❌ Windows-specific path
file_path = "C:\Users\John\Documents\data.txt"

# ❌ Hardcoded user path
with open("C:/Users/John/file.txt", "r") as f:
    data = f.read()

# ✅ Relative path - works on any computer
file_path = "data.txt"

# ✅ Use os.path.join() for cross-platform compatibility
import os
file_path = os.path.join("data", "input.txt")

# ✅ Relative to current directory
with open("input.txt", "r") as f:
    data = f.read()

# ✅ For multiple files, use relative paths
input_file = os.path.join(".", "data", "input.txt")
output_file = os.path.join(".", "data", "output.txt")

# Check Python version
import sys
print(sys.version)  # Should match submission platform

# Common submission platforms use:
# - Python 3.8 or 3.9
# - Node.js 14 or 16

# Avoid version-specific features:
# ❌ Python 3.9+ only: dict union operator (|)
# ✅ Works everywhere: dict.update() or {**dict1, **dict2}

# ❌ Python 3.8+ only: walrus operator (:=)
# ✅ Works everywhere: regular assignment

# Test with same version as submission platform
# Use pyenv or nvm to switch versions locally

# ✅ Use standard library (always available)
import os
import sys
import json
import math
import collections

# ❌ External libraries may not be available
# import pandas  # May not be allowed
# import numpy   # May not be allowed

# ✅ Check platform documentation for allowed libraries
# LeetCode: Usually only standard library
# HackerRank: Check problem requirements
# GitHub Actions: Check workflow dependencies

# If you need external library, check if it's allowed
# Some platforms allow: requests, beautifulsoup4
# Most platforms restrict: pandas, numpy, scipy

# ❌ Case mismatch - works on Windows, fails on Linux
with open("File.txt", "r") as f:  # File.txt vs file.txt
    data = f.read()

# ✅ Match exact case
with open("file.txt", "r") as f:  # Use exact filename
    data = f.read()

# ✅ Use os.path.exists() to check file
import os
if os.path.exists("input.txt"):
    with open("input.txt", "r") as f:
        data = f.read()

# ✅ List directory to find correct case
import os
files = os.listdir(".")
for file in files:
    if file.lower() == "input.txt":
        with open(file, "r") as f:  # Use actual filename
            data = f.read()

# ❌ Hardcoded values - may not exist on submission platform
api_key = os.environ.get("API_KEY")  # May be None
database_url = "localhost:5432"  # Hardcoded

# ✅ Use defaults or read from input
api_key = os.environ.get("API_KEY", "default_key")
# Or read from input file instead of environment

# ❌ Platform-specific code
if sys.platform == "win32":
    path = "C:/Users/name/file.txt"

# ✅ Cross-platform code
import os
path = os.path.join("data", "file.txt")

# ✅ Use input() or file reading instead of environment variables
# Read configuration from input file, not environment

# Test checklist:
# 1. Use relative paths only
# 2. Test with same Python/Node.js version
# 3. Use only standard library
# 4. Check file names are case-sensitive
# 5. Remove all hardcoded paths
# 6. Test with minimal input
# 7. Check for platform-specific code

# Test on Linux if submission uses Linux
# Use Docker or WSL to test Linux environment

# Example test script:
import os
import sys

# Check version
print(f"Python version: {sys.version}")

# Check current directory
print(f"Current directory: {os.getcwd()}")

# List files
print(f"Files: {os.listdir('.')}")

# Test file reading
try:
    with open("input.txt", "r") as f:
        print("File read successfully")
except FileNotFoundError:
    print("File not found - check filename case")