Download and Caching

def download(url, fpath=None, hash_prefix=None, hasher='sha512', **kwargs):
    """
    Download file from URL with progress and verification.
    
    Args:
        url (str): URL to download from
        fpath (str|Path): Local file path (auto-generated if None)
        hash_prefix (str): Expected hash prefix for verification
        hasher (str): Hash algorithm ('sha512', 'sha256', 'md5')
        verbose (int): Verbosity level
        chunk_size (int): Download chunk size in bytes
        timeout (float): Connection timeout
        
    Returns:
        str: Path to downloaded file
        
    Raises:
        URLError: Download failed
        HashMismatchError: Hash verification failed
    """

def grabdata(url, fpath=None, dpath=None, fname=None, **kwargs):
    """
    Download and cache data with automatic path handling.
    
    Args:
        url (str): URL to download
        fpath (str): Explicit file path
        dpath (str): Directory for cached file
        fname (str): Filename for cached file
        **kwargs: Additional download options
        
    Returns:
        str: Path to cached file
    """

class DownloadManager:
    """
    Manage multiple download operations with queuing and progress tracking.
    """
    def __init__(self, max_workers=4): ...
    
    def submit(self, url, fpath=None, **kwargs): ...
    def download_all(self): ...
    def __enter__(self): ...
    def __exit__(self, exc_type, exc_val, exc_tb): ...

class Cacher:
    """
    On-disk caching with dependency tracking.
    Automatically invalidates cache when dependencies change.
    """
    def __init__(self, fname, depends=None, dpath=None, appname='ubelt', **kwargs):
        """
        Args:
            fname (str): Cache filename
            depends: Dependencies that invalidate cache when changed
            dpath (str): Cache directory
            appname (str): Application name for cache organization
            **kwargs: Additional cache options
        """
    
    def tryload(self):
        """
        Try to load cached result.
        
        Returns:
            object|None: Cached result or None if cache miss/invalid
        """
    
    def save(self, data):
        """
        Save data to cache.
        
        Args:
            data: Data to cache
        """
    
    def clear(self):
        """Clear cached data."""
    
    def exists(self):
        """
        Check if cache exists and is valid.
        
        Returns:
            bool: True if cache exists and dependencies unchanged
        """
    
    def ensure(self, func, *args, **kwargs):
        """
        Ensure cached result exists, computing if necessary.
        
        Args:
            func: Function to call if cache miss
            *args: Arguments for func
            **kwargs: Keyword arguments for func
            
        Returns:
            object: Cached or computed result
        """

class CacheStamp:
    """
    Lightweight cache stamping for file-producing computations.
    Tracks when outputs are newer than inputs.
    """
    def __init__(self, fname, dpath=None, **kwargs): ...
    
    def expired(self, *depends):
        """
        Check if cache is expired relative to dependencies.
        
        Args:
            *depends: File paths or other dependencies
            
        Returns:
            bool: True if cache is expired
        """
    
    def renew(self):
        """Update cache timestamp."""
    
    def clear(self):
        """Remove cache stamp."""

import ubelt as ub

# Simple download
url = 'https://example.com/data.zip'
fpath = ub.download(url)
print(f"Downloaded to: {fpath}")

# Download with verification
url = 'https://example.com/important.tar.gz'
expected_hash = 'a1b2c3d4e5f6...'  # First few characters of expected hash
fpath = ub.download(url, hash_prefix=expected_hash, hasher='sha256')

# Download to specific location
local_path = './downloads/myfile.zip'
ub.download(url, fpath=local_path, verbose=2)

# Download with caching (won't re-download if file exists)
cached_file = ub.grabdata(url, dpath='./cache')

import ubelt as ub

# Download multiple files
urls = [
    'https://example.com/file1.zip',
    'https://example.com/file2.tar.gz',
    'https://example.com/file3.json'
]

# Sequential downloads
files = []
for url in urls:
    fpath = ub.download(url, dpath='./downloads')
    files.append(fpath)

# Parallel downloads with DownloadManager
with ub.DownloadManager(max_workers=3) as dm:
    futures = []
    for url in urls:
        future = dm.submit(url, dpath='./downloads')
        futures.append(future)
    
    # Get results
    files = [future.result() for future in futures]

import ubelt as ub
import time

def expensive_computation(n):
    """Simulate expensive computation"""
    print(f"Computing for n={n}...")
    time.sleep(2)  # Simulate work
    return n ** 2

# Basic caching
cache = ub.Cacher('computation_cache')
result = cache.tryload()
if result is None:
    result = expensive_computation(100)
    cache.save(result)
print(f"Result: {result}")

# Dependency-based caching
input_file = 'input.txt'
with open(input_file, 'w') as f:
    f.write('some input data')

# Cache depends on input file
cache = ub.Cacher('file_processing', depends=[input_file])
result = cache.tryload()
if result is None:
    # Process the file
    with open(input_file, 'r') as f:
        data = f.read()
    result = data.upper()  # Simple processing
    cache.save(result)

# Cache will be invalidated if input.txt changes

# Using ensure for cleaner code
def process_data(filename):
    with open(filename, 'r') as f:
        return f.read().upper()

cache = ub.Cacher('processing', depends=[input_file])
result = cache.ensure(process_data, input_file)

import ubelt as ub

# Stamp-based caching for file generation
input_files = ['input1.txt', 'input2.txt', 'config.json']
output_file = 'processed_output.json'

stamp = ub.CacheStamp('processing_stamp')

if stamp.expired(*input_files, output_file):
    print("Processing files...")
    # Do expensive file processing
    processed_data = {'result': 'processed'}
    
    # Write output
    import json
    with open(output_file, 'w') as f:
        json.dump(processed_data, f)
    
    # Update stamp
    stamp.renew()
else:
    print("Using cached output")

# Output file exists and is newer than inputs

import ubelt as ub

# Cache with custom dependencies
def get_data_hash():
    """Get hash of current data state"""
    return ub.hash_data({'version': '1.2', 'config': 'prod'})

# Cache that depends on data state, not just files
cache = ub.Cacher('model_cache', depends=[get_data_hash()])

def train_model():
    print("Training model...")
    return {'accuracy': 0.95, 'model': 'trained_weights'}

model = cache.ensure(train_model)

# Organized caching with app-specific directories
user_cache = ub.Cacher('user_prefs', appname='myapp')
model_cache = ub.Cacher('models', appname='myapp', dpath='./models')

# Clear caches when needed
if need_fresh_data:
    cache.clear()
    
# Check cache status
if cache.exists():
    print("Cache is valid")
    data = cache.tryload()
else:
    print("Cache expired or missing")