diff --git a/tests/test_btc_address.py b/tests/test_btc_address.py
index 68d09f67..5ba1fc0d 100644
--- a/tests/test_btc_address.py
+++ b/tests/test_btc_address.py
@@ -1,35 +1,41 @@
+"""Test BTC address."""
 # -*- coding: utf-8 -*-
+
+# standard
 import pytest
 
+# local
 from validators import btc_address, ValidationFailure
 
 
 @pytest.mark.parametrize(
-    'value',
+    "value",
     [
         # P2PKH (Pay-to-PubkeyHash) type
-        '1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2',
+        "1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2",
         # P2SH (Pay to script hash) type
-        '3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy',
+        "3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy",
         # Bech32/segwit type
-        'bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq',
-        'bc1qc7slrfxkknqcq2jevvvkdgvrt8080852dfjewde450xdlk4ugp7szw5tk9',
+        "bc1qar0srrr7xfkvy5l643lydnw9re59gtzzwf5mdq",
+        "bc1qc7slrfxkknqcq2jevvvkdgvrt8080852dfjewde450xdlk4ugp7szw5tk9",
     ],
 )
-def test_returns_true_on_valid_btc_address(value):
+def test_returns_true_on_valid_btc_address(value: str):
+    """Test returns true on valid btc address."""
     assert btc_address(value)
 
 
 @pytest.mark.parametrize(
-    'value',
+    "value",
     [
-        'ff3Cwgr2g7vsi1bXDUkpEnVoRLA9w4FZfC69',
-        'b3Cgwgr2g7vsi1bXyjyDUkphEnVoRLA9w4FZfC69',
+        "ff3Cwgr2g7vsi1bXDUkpEnVoRLA9w4FZfC69",
+        "b3Cgwgr2g7vsi1bXyjyDUkphEnVoRLA9w4FZfC69",
         # incorrect header
-        '1BvBMsEYstWetqTFn5Au4m4GFg7xJaNVN2',
+        "1BvBMsEYstWetqTFn5Au4m4GFg7xJaNVN2",
         # incorrect checksum
-        '3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLz',
+        "3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLz",
     ],
 )
-def test_returns_failed_validation_on_invalid_btc_address(value):
+def test_returns_failed_validation_on_invalid_btc_address(value: str):
+    """Test returns failed validation on invalid btc address."""
     assert isinstance(btc_address(value), ValidationFailure)
diff --git a/validators/btc_address.py b/validators/btc_address.py
index 35ada853..a4984c54 100644
--- a/validators/btc_address.py
+++ b/validators/btc_address.py
@@ -1,55 +1,61 @@
-import re
+"""BTC Address."""
+# -*- coding: utf-8 -*-
+
+# standard
 from hashlib import sha256
+import re
 
+# local
 from .utils import validator
 
-segwit_pattern = re.compile(
-    r'^(bc|tc)[0-3][02-9ac-hj-np-z]{14,74}$')
-
-
-def validate_segwit_address(addr):
-    return segwit_pattern.match(addr)
+_segwit_pattern = re.compile(r"^(bc|tc)[0-3][02-9ac-hj-np-z]{14,74}$")
 
 
-def decode_base58(addr):
+def _decode_base58(addr: str):
+    """Decode base58."""
     alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
-    return sum([
-        (58 ** e) * alphabet.index(i)
-        for e, i in enumerate(addr[::-1])
-    ])
+    return sum((58**enm) * alphabet.index(idx) for enm, idx in enumerate(addr[::-1]))
 
 
-def validate_old_btc_address(addr):
-    "Validate P2PKH and P2SH type address"
-    if not len(addr) in range(25, 35):
+def _validate_old_btc_address(addr: str):
+    """Validate P2PKH and P2SH type address."""
+    if len(addr) not in range(25, 35):
         return False
-    decoded_bytes = decode_base58(addr).to_bytes(25, "big")
-    header = decoded_bytes[:-4]
-    checksum = decoded_bytes[-4:]
+    decoded_bytes = _decode_base58(addr).to_bytes(25, "big")
+    header, checksum = decoded_bytes[:-4], decoded_bytes[-4:]
     return checksum == sha256(sha256(header).digest()).digest()[:4]
 
 
 @validator
-def btc_address(value):
-    """
-    Return whether or not given value is a valid bitcoin address.
-
-    If the value is valid bitcoin address this function returns ``True``,
-    otherwise :class:`~validators.utils.ValidationFailure`.
+def btc_address(value: str, /):
+    """Return whether or not given value is a valid bitcoin address.
 
     Full validation is implemented for P2PKH and P2SH addresses.
-    For segwit addresses a regexp is used to provide a reasonable estimate
-    on whether the address is valid.
+    For segwit addresses a regexp is used to provide a reasonable
+    estimate on whether the address is valid.
 
     Examples::
 
         >>> btc_address('3Cwgr2g7vsi1bXDUkpEnVoRLA9w4FZfC69')
-        True
+        # Output: True
+        >>> btc_address('1BvBMsEYstWetqTFn5Au4m4GFg7xJaNVN2')
+        # Output: ValidationFailure(func=btc_address, args=...)
+
+    Args:
+        `value`:
+            [Required] Bitcoin address string to validate.
+
+    Returns:
+        `True`:
+            If the value is valid bitcoin address.
+        `ValidationFailure`:
+            If the value is an invalid bitcoin address.
 
-    :param value: Bitcoin address string to validate
     """
-    if not value or not isinstance(value, str):
-        return False
-    if value[:2] in ("bc", "tb"):
-        return validate_segwit_address(value)
-    return validate_old_btc_address(value)
+    if value and type(value) is str:
+        return (
+            _segwit_pattern.match(value)
+            if value[:2] in ("bc", "tb")
+            else _validate_old_btc_address(value)
+        )
+    return False