From b2d3f333f084012b2cedafc9d6e04ccdc0ee09bd Mon Sep 17 00:00:00 2001
From: Eric Jolibois <em.jolibois@gmail.com>
Date: Tue, 2 Mar 2021 13:05:57 +0100
Subject: [PATCH] refactor: set `Pattern` encoder in `ENCODERS_BY_TYPE` (#2444)

* refactor: set `Pattern` encoder in `ENCODERS_BY_TYPE`

* docs: add change file
---
 changes/2444-PrettyWood.md |  1 +
 pydantic/json.py           | 14 ++++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 changes/2444-PrettyWood.md

diff --git a/changes/2444-PrettyWood.md b/changes/2444-PrettyWood.md
new file mode 100644
index 0000000000..0d7b9afbf3
--- /dev/null
+++ b/changes/2444-PrettyWood.md
@@ -0,0 +1 @@
+expose `Pattern` encoder to `fastapi`
diff --git a/pydantic/json.py b/pydantic/json.py
index 9777a62eb4..81b2698101 100644
--- a/pydantic/json.py
+++ b/pydantic/json.py
@@ -1,13 +1,21 @@
 import datetime
+import re
+import sys
 from collections import deque
 from decimal import Decimal
 from enum import Enum
 from ipaddress import IPv4Address, IPv4Interface, IPv4Network, IPv6Address, IPv6Interface, IPv6Network
 from pathlib import Path
 from types import GeneratorType
-from typing import Any, Callable, Dict, Pattern, Type, Union
+from typing import Any, Callable, Dict, Type, Union
 from uuid import UUID
 
+if sys.version_info >= (3, 7):
+    Pattern = re.Pattern
+else:
+    # python 3.6
+    Pattern = re.compile('a').__class__
+
 from .color import Color
 from .types import SecretBytes, SecretStr
 
@@ -58,6 +66,7 @@ def decimal_encoder(dec_value: Decimal) -> Union[int, float]:
     IPv6Interface: str,
     IPv6Network: str,
     Path: str,
+    Pattern: lambda o: o.pattern,
     SecretBytes: str,
     SecretStr: str,
     set: list,
@@ -75,9 +84,6 @@ def pydantic_encoder(obj: Any) -> Any:
     elif is_dataclass(obj):
         return asdict(obj)
 
-    if isinstance(obj, Pattern):
-        return obj.pattern
-
     # Check the class type and its superclasses for a matching encoder
     for base in obj.__class__.__mro__[:-1]:
         try: