Add env_nested_max_split setting (#534)

docs/index.md

@@ -324,6 +324,58 @@ print(Settings().model_dump())
 `env_nested_delimiter` can be configured via the `model_config` as shown above, or via the
 `_env_nested_delimiter` keyword argument on instantiation.
 
+By default environment variables are split by `env_nested_delimiter` into arbitrarily deep nested fields. You can limit
+the depth of the nested fields with the `env_nested_max_split` config setting. A common use case this is particularly useful
+is for two-level deep settings, where the `env_nested_delimiter` (usually a single `_`) may be a substring of model
+field names. For example:
+
+```bash
+# your environment
+export GENERATION_LLM_PROVIDER='anthropic'
+export GENERATION_LLM_API_KEY='your-api-key'
+export GENERATION_LLM_API_VERSION='2024-03-15'
+```
+
+You could load them into the following settings model:
+
+```py
+from pydantic import BaseModel
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class LLMConfig(BaseModel):
+    provider: str = 'openai'
+    api_key: str
+    api_type: str = 'azure'
+    api_version: str = '2023-03-15-preview'
+
+
+class GenerationConfig(BaseSettings):
+    model_config = SettingsConfigDict(
+        env_nested_delimiter='_', env_nested_max_split=1, env_prefix='GENERATION_'
+    )
+
+    llm: LLMConfig
+    ...
+
+
+print(GenerationConfig().model_dump())
+"""
+{
+    'llm': {
+        'provider': 'anthropic',
+        'api_key': 'your-api-key',
+        'api_type': 'azure',
+        'api_version': '2024-03-15',
+    }
+}
+"""
+```
+
+Without `env_nested_max_split=1` set, `GENERATION_LLM_API_KEY` would be parsed as `llm.api.key` instead of `llm.api_key`
+and it would raise a `ValidationError`.
+
 Nested environment variables take precedence over the top-level environment variable JSON
 (e.g. in the example above, `SUB_MODEL__V2` trumps `SUB_MODEL`).
 

pydantic_settings/main.py

@@ -38,6 +38,7 @@ class SettingsConfigDict(ConfigDict, total=False):
     env_file_encoding: str | None
     env_ignore_empty: bool
     env_nested_delimiter: str | None
+    env_nested_max_split: int | None
     env_parse_none_str: str | None
     env_parse_enums: bool | None
     cli_prog_name: str | None
@@ -112,6 +113,7 @@ class BaseSettings(BaseModel):
         _env_file_encoding: The env file encoding, e.g. `'latin-1'`. Defaults to `None`.
         _env_ignore_empty: Ignore environment variables where the value is an empty string. Default to `False`.
         _env_nested_delimiter: The nested env values delimiter. Defaults to `None`.
+        _env_nested_max_split: The nested env values maximum nesting. Defaults to `None`, which means no limit.
         _env_parse_none_str: The env string value that should be parsed (e.g. "null", "void", "None", etc.)
             into `None` type(None). Defaults to `None` type(None), which means no parsing should occur.
         _env_parse_enums: Parse enum field names to values. Defaults to `None.`, which means no parsing should occur.
@@ -148,6 +150,7 @@ def __init__(
         _env_file_encoding: str | None = None,
         _env_ignore_empty: bool | None = None,
         _env_nested_delimiter: str | None = None,
+        _env_nested_max_split: int | None = None,
         _env_parse_none_str: str | None = None,
         _env_parse_enums: bool | None = None,
         _cli_prog_name: str | None = None,
@@ -178,6 +181,7 @@ def __init__(
                 _env_file_encoding=_env_file_encoding,
                 _env_ignore_empty=_env_ignore_empty,
                 _env_nested_delimiter=_env_nested_delimiter,
+                _env_nested_max_split=_env_nested_max_split,
                 _env_parse_none_str=_env_parse_none_str,
                 _env_parse_enums=_env_parse_enums,
                 _cli_prog_name=_cli_prog_name,
@@ -232,6 +236,7 @@ def _settings_build_values(
         _env_file_encoding: str | None = None,
         _env_ignore_empty: bool | None = None,
         _env_nested_delimiter: str | None = None,
+        _env_nested_max_split: int | None = None,
         _env_parse_none_str: str | None = None,
         _env_parse_enums: bool | None = None,
         _cli_prog_name: str | None = None,
@@ -270,6 +275,11 @@ def _settings_build_values(
             if _env_nested_delimiter is not None
             else self.model_config.get('env_nested_delimiter')
         )
+        env_nested_max_split = (
+            _env_nested_max_split
+            if _env_nested_max_split is not None
+            else self.model_config.get('env_nested_max_split')
+        )
         env_parse_none_str = (
             _env_parse_none_str if _env_parse_none_str is not None else self.model_config.get('env_parse_none_str')
         )
@@ -333,6 +343,7 @@ def _settings_build_values(
             case_sensitive=case_sensitive,
             env_prefix=env_prefix,
             env_nested_delimiter=env_nested_delimiter,
+            env_nested_max_split=env_nested_max_split,
             env_ignore_empty=env_ignore_empty,
             env_parse_none_str=env_parse_none_str,
             env_parse_enums=env_parse_enums,
@@ -344,6 +355,7 @@ def _settings_build_values(
             case_sensitive=case_sensitive,
             env_prefix=env_prefix,
             env_nested_delimiter=env_nested_delimiter,
+            env_nested_max_split=env_nested_max_split,
             env_ignore_empty=env_ignore_empty,
             env_parse_none_str=env_parse_none_str,
             env_parse_enums=env_parse_enums,
@@ -412,6 +424,7 @@ def _settings_build_values(
         env_file_encoding=None,
         env_ignore_empty=False,
         env_nested_delimiter=None,
+        env_nested_max_split=None,
         env_parse_none_str=None,
         env_parse_enums=None,
         cli_prog_name=None,

pydantic_settings/sources.py

@@ -735,6 +735,7 @@ def __init__(
         case_sensitive: bool | None = None,
         env_prefix: str | None = None,
         env_nested_delimiter: str | None = None,
+        env_nested_max_split: int | None = None,
         env_ignore_empty: bool | None = None,
         env_parse_none_str: str | None = None,
         env_parse_enums: bool | None = None,
@@ -745,6 +746,10 @@ def __init__(
         self.env_nested_delimiter = (
             env_nested_delimiter if env_nested_delimiter is not None else self.config.get('env_nested_delimiter')
         )
+        self.env_nested_max_split = (
+            env_nested_max_split if env_nested_max_split is not None else self.config.get('env_nested_max_split')
+        )
+        self.maxsplit = (self.env_nested_max_split or 0) - 1
         self.env_prefix_len = len(self.env_prefix)
 
         self.env_vars = self._load_env_vars()
@@ -910,11 +915,13 @@ def explode_env_vars(self, field_name: str, field: FieldInfo, env_vars: Mapping[
         ]
         result: dict[str, Any] = {}
         for env_name, env_val in env_vars.items():
-            if not any(env_name.startswith(prefix) for prefix in prefixes):
+            try:
+                prefix = next(prefix for prefix in prefixes if env_name.startswith(prefix))
+            except StopIteration:
                 continue
             # we remove the prefix before splitting in case the prefix has characters in common with the delimiter
-            env_name_without_prefix = env_name[self.env_prefix_len :]
-            _, *keys, last_key = env_name_without_prefix.split(self.env_nested_delimiter)
+            env_name_without_prefix = env_name[len(prefix) :]
+            *keys, last_key = env_name_without_prefix.split(self.env_nested_delimiter, self.maxsplit)
             env_var = result
             target_field: FieldInfo | None = field
             for key in keys:
@@ -964,6 +971,7 @@ def __init__(
         case_sensitive: bool | None = None,
         env_prefix: str | None = None,
         env_nested_delimiter: str | None = None,
+        env_nested_max_split: int | None = None,
         env_ignore_empty: bool | None = None,
         env_parse_none_str: str | None = None,
         env_parse_enums: bool | None = None,
@@ -977,6 +985,7 @@ def __init__(
             case_sensitive,
             env_prefix,
             env_nested_delimiter,
+            env_nested_max_split,
             env_ignore_empty,
             env_parse_none_str,
             env_parse_enums,

tests/conftest.py

@@ -79,6 +79,11 @@ def docs_test_env():
     setenv.set('SUB_MODEL__V3', '3')
     setenv.set('SUB_MODEL__DEEP__V4', 'v4')
 
+    # envs for parsing environment variable values example with env_nested_max_split=1
+    setenv.set('GENERATION_LLM_PROVIDER', 'anthropic')
+    setenv.set('GENERATION_LLM_API_KEY', 'your-api-key')
+    setenv.set('GENERATION_LLM_API_VERSION', '2024-03-15')
+
     yield setenv
 
     setenv.clear()

tests/test_settings.py

@@ -4,7 +4,7 @@
 import pathlib
 import sys
 import uuid
-from datetime import datetime, timezone
+from datetime import date, datetime, timezone
 from enum import IntEnum
 from pathlib import Path
 from typing import Any, Callable, Dict, Generic, Hashable, List, Optional, Set, Tuple, Type, TypeVar, Union
@@ -398,6 +398,40 @@ class Cfg(BaseSettings):
     assert Cfg().model_dump() == {'sub_model': {'v1': '-1-', 'v2': '-2-'}}
 
 
+@pytest.mark.parametrize('env_prefix', [None, 'prefix_', 'prefix__'])
+def test_nested_env_max_split(env, env_prefix):
+    class Person(BaseModel):
+        sex: Literal['M', 'F']
+        first_name: str
+        date_of_birth: date
+
+    class Cfg(BaseSettings):
+        caregiver: Person
+        significant_other: Optional[Person] = None
+        next_of_kin: Optional[Person] = None
+
+        model_config = SettingsConfigDict(env_nested_delimiter='_', env_nested_max_split=1)
+        if env_prefix is not None:
+            model_config['env_prefix'] = env_prefix
+
+    env_prefix = env_prefix or ''
+    env.set(env_prefix + 'caregiver_sex', 'M')
+    env.set(env_prefix + 'caregiver_first_name', 'Joe')
+    env.set(env_prefix + 'caregiver_date_of_birth', '1975-09-12')
+    env.set(env_prefix + 'significant_other_sex', 'F')
+    env.set(env_prefix + 'significant_other_first_name', 'Jill')
+    env.set(env_prefix + 'significant_other_date_of_birth', '1998-04-19')
+    env.set(env_prefix + 'next_of_kin_sex', 'M')
+    env.set(env_prefix + 'next_of_kin_first_name', 'Jack')
+    env.set(env_prefix + 'next_of_kin_date_of_birth', '1999-04-19')
+
+    assert Cfg().model_dump() == {
+        'caregiver': {'sex': 'M', 'first_name': 'Joe', 'date_of_birth': date(1975, 9, 12)},
+        'significant_other': {'sex': 'F', 'first_name': 'Jill', 'date_of_birth': date(1998, 4, 19)},
+        'next_of_kin': {'sex': 'M', 'first_name': 'Jack', 'date_of_birth': date(1999, 4, 19)},
+    }
+
+
 class DateModel(BaseModel):
     pips: bool = False