cshelve 0.3.0

Propulsing the shelve module to the cloud

Cloud Shelve

Cloud Shelve (cshelve) is a Python package that provides a seamless way to store and manage data in the cloud using the familiar Python Shelve interface. It is designed for efficient and scalable storage solutions, allowing you to leverage cloud providers for persistent storage while keeping the simplicity of the shelve API.

Features

• Supports large file storage in the cloud
• Secure data in-transit encryption when using cloud storage
• Fully compatible with Python's shelve API
• Cross-platform compatibility for local and remote storage

Installation

Install cshelve via pip:

pip install cshelve

Usage

The cshelve module strictly follows the official shelve API. Consequently, you can refer to the Python official documentation for general usage examples. Simply replace the shelve import with cshelve, and you're good to go.

Local Storage

Here is an example, adapted from the official shelve documentation, demonstrating local storage usage. Just replace shelve with cshelve:

import cshelve

d = cshelve.open('local.db')  # Open the local database file

key = 'key'
data = 'data'

d[key] = data                 # Store data at the key (overwrites existing data)
data = d[key]                 # Retrieve a copy of data (raises KeyError if not found)
del d[key]                    # Delete data at the key (raises KeyError if not found)

flag = key in d               # Check if the key exists in the database
klist = list(d.keys())        # List all existing keys (could be slow for large datasets)

# Note: Since writeback=True is not used, handle data carefully:
d['xx'] = [0, 1, 2]           # Store a list
d['xx'].append(3)             # This won't persist since writeback=True is not used

# Correct approach:
temp = d['xx']                # Extract the stored list
temp.append(5)                # Modify the list
d['xx'] = temp                # Store it back to persist changes

d.close()                     # Close the database

Debug Storage

For testing purposes, it is possible to use an in-memory provider that can:

• Persist the data during all the program execution.
• Remove the data object is deleted.

Here is a configuration example:

$ cat in-memory.ini
[default]
provider    = in-memory
# If set, open twice the same database during the program execution will lead to open twice the same database.
persist-key = standard

A common use case for this provider is to simplify mocking.

Example:

$ cat persist.ini
[default]
provider    = in-memory
# If set, open twice the same database during the program execution will lead to open twice the same database.
persist-key = my-db

$ cat do-not-persist.ini
[default]
provider = in-memory

import cshelve

with cshelve.open('persist.ini') as db:
    db["Asterix"] = "Gaulois"

with cshelve.open('persist.ini') as db:
    assert db["Asterix"] == "Gaulois"

with cshelve.open('do-not-persist.ini') as db:
    db["Obelix"] = "Gaulois"

with cshelve.open('do-not-persist.ini') as db:
    assert "Obelix" not in db

Remote Storage (e.g., Azure)

To configure remote cloud storage, you need to provide an INI file containing your cloud provider's configuration. The file should have a .ini extension.

Example Azure Blob Configuration

$ cat azure-blob.ini
[default]
provider        = azure-blob
account_url     = https://myaccount.blob.core.windows.net
auth_type       = passwordless
container_name  = mycontainer

Once the INI file is ready, you can interact with remote storage the same way as with local storage. Here's an example using Azure:

import cshelve

d = cshelve.open('azure-blob.ini')  # Open using the remote storage configuration

key = 'key'
data = 'data'

d[key] = data                  # Store data at the key
data = d[key]                  # Retrieve the data
del d[key]                     # Delete the data

flag = key in d                # Check if the key exists in the cloud store
klist = list(d.keys())         # List all keys in the remote storage

d['xx'] = [0, 1, 2]            # Store a list remotely
d['xx'].append(3)              # Changes to the list won't persist

# Correct approach:
temp = d['xx']                 # Extract the stored list
temp.append(5)                 # Modify the list
d['xx'] = temp                 # Store it back to persist changes

d.close()                      # Close the connection to the remote store

More configuration examples for other cloud providers can be found here.

Providers configuration

In Memory

Provider: in-memory

The In Memory provider uses an in-memory data structure to simulate storage. This is useful for testing and development purposes.

Option	Description	Required	Default Value
persist-key	If set, its value will be conserved and reused during the program execution.	:x:	None
exists	If True, the database exists; otherwise, it will be created.	:x:	False

Azure Blob

Provider: azure-blob

The Azure provider uses Azure Blob Storage as remote storage. The module considers the provided container as dedicated to the application. The impact might be significant. For example, if the flag n is provided to the open function, the entire container will be purged, aligning with the official interface.

Option	Description	Required	Default Value
account_url	The URL of your Azure storage account.	:x:
auth_type	The authentication method to use: access_key, passwordless, connection_string or anonymous.	:white_check_mark:
container_name	The name of the container in your Azure storage account.	:white_check_mark:

Depending on the open flag, the permissions required by cshelve for blob storage vary.

Flag	Description	Permissions Needed
r	Open an existing blob storage container for reading only.	Storage Blob Data Reader
w	Open an existing blob storage container for reading and writing.	Storage Blob Data Contributor
c	Open a blob storage container for reading and writing, creating it if it doesn't exist.	Storage Blob Data Contributor
n	Purge the blob storage container before using it.	Storage Blob Data Contributor

Authentication type supported:

Auth Type	Description	Advantage	Disadvantage	Example Configuration
Access Key	Uses an Access Key or a Shared Access Signature for authentication.	Fast startup as no additional credential retrieval is needed.	Credentials need to be securely managed and provided.	Example
Anonymous	No authentication for anonymous access on public blob storage.	No configuration or credentials needed.	Read-only access.	Example
Connection String	Uses a connection string for authentication. Credentials are provided directly in the string.	Fast startup as no additional credential retrieval is needed.	Credentials need to be securely managed and provided.	Example
Passwordless	Uses passwordless authentication methods such as Managed Identity.	Recommended for better security and easier credential management.	May impact startup time due to the need to retrieve authentication credentials.	Example

Contributing

We welcome contributions from the community! Have a look at our issues.

License

This project is licensed under the MIT License. See the LICENSE file for more details.

Contact

If you have any questions, issues, or feedback, feel free to [open an issue]https://github.com/Standard-Cloud/cshelve/issues).