From aa3ac27e1fb6bb9c61cad88e2c0c92b9f4e6b7a7 Mon Sep 17 00:00:00 2001
From: AlexTereshenkov <50622389+AlexTereshenkov@users.noreply.github.com>
Date: Wed, 5 Jun 2019 10:24:28 +0100
Subject: [PATCH 1/4] Remove redundant check arr_or_dtype is None

Checking whether `if arr_or_dtype is None:` is done in the beginning of the function so the following check is redundant and can be safely removed
---
 pandas/core/dtypes/common.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/pandas/core/dtypes/common.py b/pandas/core/dtypes/common.py
index b5cd73a81962b..8e67ef1c14cdf 100644
--- a/pandas/core/dtypes/common.py
+++ b/pandas/core/dtypes/common.py
@@ -1902,8 +1902,6 @@ def _is_dtype_type(arr_or_dtype, condition):
         if issubclass(arr_or_dtype, ExtensionDtype):
             arr_or_dtype = arr_or_dtype.type
         return condition(np.dtype(arr_or_dtype).type)
-    elif arr_or_dtype is None:
-        return condition(type(None))
 
     # if we have an array-like
     if hasattr(arr_or_dtype, 'dtype'):

From 44b521d9e932d9e4a57f3837e3a4bd9bf5641bb9 Mon Sep 17 00:00:00 2001
From: AlexTereshenkov <50622389+AlexTereshenkov@users.noreply.github.com>
Date: Wed, 5 Jun 2019 12:12:05 +0100
Subject: [PATCH 2/4] Keeping the check under the fastpath block

Keeping the check under the fastpath block so all fastpaths are collected.
---
 pandas/core/dtypes/common.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/pandas/core/dtypes/common.py b/pandas/core/dtypes/common.py
index 8e67ef1c14cdf..24210154a3f16 100644
--- a/pandas/core/dtypes/common.py
+++ b/pandas/core/dtypes/common.py
@@ -1892,9 +1892,6 @@ def _is_dtype_type(arr_or_dtype, condition):
     bool : if the condition is satisifed for the arr_or_dtype
     """
 
-    if arr_or_dtype is None:
-        return condition(type(None))
-
     # fastpath
     if isinstance(arr_or_dtype, np.dtype):
         return condition(arr_or_dtype.type)
@@ -1902,7 +1899,9 @@ def _is_dtype_type(arr_or_dtype, condition):
         if issubclass(arr_or_dtype, ExtensionDtype):
             arr_or_dtype = arr_or_dtype.type
         return condition(np.dtype(arr_or_dtype).type)
-
+    elif arr_or_dtype is None:
+        return condition(type(None))
+    
     # if we have an array-like
     if hasattr(arr_or_dtype, 'dtype'):
         arr_or_dtype = arr_or_dtype.dtype

From b8f1357388e4eb52bfef3ae0e37fba90502a0787 Mon Sep 17 00:00:00 2001
From: AlexTereshenkov <50622389+AlexTereshenkov@users.noreply.github.com>
Date: Wed, 5 Jun 2019 12:14:39 +0100
Subject: [PATCH 3/4] Strip whitespace

Strip whitespace
---
 pandas/core/dtypes/common.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/dtypes/common.py b/pandas/core/dtypes/common.py
index 24210154a3f16..aa2cc3053ac65 100644
--- a/pandas/core/dtypes/common.py
+++ b/pandas/core/dtypes/common.py
@@ -1901,7 +1901,7 @@ def _is_dtype_type(arr_or_dtype, condition):
         return condition(np.dtype(arr_or_dtype).type)
     elif arr_or_dtype is None:
         return condition(type(None))
-    
+
     # if we have an array-like
     if hasattr(arr_or_dtype, 'dtype'):
         arr_or_dtype = arr_or_dtype.dtype

From 1524eb8acf9665d29ee3cc98208fd3bde6869325 Mon Sep 17 00:00:00 2001
From: AlexTereshenkov <50622389+AlexTereshenkov@users.noreply.github.com>
Date: Wed, 5 Jun 2019 13:42:35 +0100
Subject: [PATCH 4/4] Moving the check

Moving the check
---
 pandas/core/dtypes/common.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/core/dtypes/common.py b/pandas/core/dtypes/common.py
index aa2cc3053ac65..8e67ef1c14cdf 100644
--- a/pandas/core/dtypes/common.py
+++ b/pandas/core/dtypes/common.py
@@ -1892,6 +1892,9 @@ def _is_dtype_type(arr_or_dtype, condition):
     bool : if the condition is satisifed for the arr_or_dtype
     """
 
+    if arr_or_dtype is None:
+        return condition(type(None))
+
     # fastpath
     if isinstance(arr_or_dtype, np.dtype):
         return condition(arr_or_dtype.type)
@@ -1899,8 +1902,6 @@ def _is_dtype_type(arr_or_dtype, condition):
         if issubclass(arr_or_dtype, ExtensionDtype):
             arr_or_dtype = arr_or_dtype.type
         return condition(np.dtype(arr_or_dtype).type)
-    elif arr_or_dtype is None:
-        return condition(type(None))
 
     # if we have an array-like
     if hasattr(arr_or_dtype, 'dtype'):