<｜begin▁of▁sentence｜>### Instruction:
As a helpful assistant, I can provide guidance on using the Configuration class in the igraph library to adjust igraph's settings programmatically. Additionally, I can assist in checking for specific settings, retrieving their current values, and saving the modified configuration to a file.

For instance, imagine a scenario where a legal secretary is tasked with managing a network of legal professionals within a law firm. They need to customize the visual representation of the network using igraph to display different types of connections between lawyers, clients, and legal cases. The legal secretary may need to adjust settings such as edge color, vertex shape, or layout parameters programmatically using the Configuration class. Additionally, the ability to save the modified configuration to a file allows for easy replication across different networks being analyzed.
### Response:
from igraph import Configuration

# Get the singleton configuration instance
config = Configuration.instance()

# Set a new value for a configuration key
config['plotting.backend'] = 'matplotlib'

# Check if a configuration key exists
if 'shells' in config:
    print('Shells configuration is present.')

# Retrieve the value of a configuration key
verbose_setting = config['general.verbose']
print(f'Verbose setting: {verbose_setting}')

# Save the current configuration to a file
with open('igraph_config.json', 'w') as f:
    config.save(f)
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