wehub-resource-sync
163 lines
3.9 KiB
Markdown
163 lines
3.9 KiB
Markdown
# python-configuration — detailed worked examples
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## Advanced Patterns
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### Pattern 5: Type Coercion
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Pydantic handles common conversions automatically.
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```python
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from pydantic_settings import BaseSettings
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from pydantic import Field, field_validator
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class Settings(BaseSettings):
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# Automatically converts "true", "1", "yes" to True
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debug: bool = False
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# Automatically converts string to int
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max_connections: int = 100
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# Parse comma-separated string to list
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allowed_hosts: list[str] = Field(default_factory=list)
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@field_validator("allowed_hosts", mode="before")
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@classmethod
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def parse_allowed_hosts(cls, v: str | list[str]) -> list[str]:
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if isinstance(v, str):
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return [host.strip() for host in v.split(",") if host.strip()]
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return v
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```
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Usage:
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```bash
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ALLOWED_HOSTS=example.com,api.example.com,localhost
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MAX_CONNECTIONS=50
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DEBUG=true
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```
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### Pattern 6: Environment-Specific Configuration
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Use an environment enum to switch behavior.
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```python
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from enum import Enum
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from pydantic_settings import BaseSettings
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from pydantic import Field, computed_field
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class Environment(str, Enum):
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LOCAL = "local"
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STAGING = "staging"
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PRODUCTION = "production"
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class Settings(BaseSettings):
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environment: Environment = Field(
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default=Environment.LOCAL,
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alias="ENVIRONMENT",
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)
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# Settings that vary by environment
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log_level: str = Field(default="DEBUG", alias="LOG_LEVEL")
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@computed_field
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@property
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def is_production(self) -> bool:
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return self.environment == Environment.PRODUCTION
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@computed_field
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@property
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def is_local(self) -> bool:
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return self.environment == Environment.LOCAL
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# Usage
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if settings.is_production:
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configure_production_logging()
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else:
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configure_debug_logging()
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```
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### Pattern 7: Nested Configuration Groups
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Organize related settings into nested models.
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```python
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from pydantic import BaseModel
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from pydantic_settings import BaseSettings
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class DatabaseSettings(BaseModel):
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host: str = "localhost"
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port: int = 5432
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name: str
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user: str
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password: str
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class RedisSettings(BaseModel):
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url: str = "redis://localhost:6379"
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max_connections: int = 10
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class Settings(BaseSettings):
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database: DatabaseSettings
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redis: RedisSettings
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debug: bool = False
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model_config = {
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"env_nested_delimiter": "__",
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"env_file": ".env",
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}
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```
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Environment variables use double underscore for nesting:
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```bash
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DATABASE__HOST=db.example.com
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DATABASE__PORT=5432
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DATABASE__NAME=myapp
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DATABASE__USER=admin
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DATABASE__PASSWORD=secret
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REDIS__URL=redis://redis.example.com:6379
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```
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### Pattern 8: Secrets from Files
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For container environments, read secrets from mounted files.
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```python
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from pydantic_settings import BaseSettings
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from pydantic import Field
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from pathlib import Path
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class Settings(BaseSettings):
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# Read from environment variable or file
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db_password: str = Field(alias="DB_PASSWORD")
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model_config = {
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"secrets_dir": "/run/secrets", # Docker secrets location
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}
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```
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Pydantic will look for `/run/secrets/db_password` if the env var isn't set.
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### Pattern 9: Configuration Validation
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Add custom validation for complex requirements.
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```python
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from pydantic_settings import BaseSettings
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from pydantic import Field, model_validator
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class Settings(BaseSettings):
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db_host: str = Field(alias="DB_HOST")
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db_port: int = Field(alias="DB_PORT")
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read_replica_host: str | None = Field(default=None, alias="READ_REPLICA_HOST")
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read_replica_port: int = Field(default=5432, alias="READ_REPLICA_PORT")
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@model_validator(mode="after")
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def validate_replica_settings(self):
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if self.read_replica_host and self.read_replica_port == self.db_port:
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if self.read_replica_host == self.db_host:
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raise ValueError(
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"Read replica cannot be the same as primary database"
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)
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return self
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```
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