CLN: assorted cleanups in cython (#46861)

Author: jbrockmendel

pandas/_libs/algos.pyx

@@ -1,6 +1,5 @@
-import cython
-from cython import Py_ssize_t
-
+cimport cython
+from cython cimport Py_ssize_t
 from libc.math cimport (
     fabs,
     sqrt,

pandas/_libs/groupby.pyx

@@ -1,7 +1,8 @@
-import cython
-from cython import Py_ssize_t
-
-from cython cimport floating
+cimport cython
+from cython cimport (
+    Py_ssize_t,
+    floating,
+)
 from libc.stdlib cimport (
     free,
     malloc,
@@ -268,7 +269,6 @@ def group_cumsum(
                         out[i, j] = na_val
                         continue
 
-
                 if isna_entry:
                     out[i, j] = na_val
                     if not skipna:
@@ -1220,7 +1220,7 @@ def group_nth(
                         if nobs[lab, j] == rank:
                             resx[lab, j] = val
 
-            # TODO: de-dup this whoel block with group_last?
+            # TODO: de-dup this whole block with group_last?
             for i in range(ncounts):
                 for j in range(K):
                     if nobs[i, j] < min_count:
@@ -1232,6 +1232,9 @@ def group_nth(
                         #  set a placeholder value in out[i, j].
                         if uses_mask:
                             result_mask[i, j] = True
+                            # set out[i, j] to 0 to be deterministic, as
+                            #  it was initialized with np.empty. Also ensures
+                            #  we can downcast out if appropriate.
                             out[i, j] = 0
                         elif numeric_object_t is float32_t or numeric_object_t is float64_t:
                             out[i, j] = NAN
@@ -1369,7 +1372,7 @@ cdef group_min_max(
     """
     cdef:
         Py_ssize_t i, j, N, K, lab, ngroups = len(counts)
-        numeric_t val, nan_val
+        numeric_t val
         ndarray[numeric_t, ndim=2] group_min_or_max
         int64_t[:, ::1] nobs
         bint uses_mask = mask is not None
@@ -1386,20 +1389,6 @@ cdef group_min_max(
     group_min_or_max = np.empty_like(out)
     group_min_or_max[:] = _get_min_or_max(<numeric_t>0, compute_max, is_datetimelike)
 
-    # NB: We do not define nan_val because there is no such thing
-    # for uint64_t.  We carefully avoid having to reference it in this
-    # case.
-    if numeric_t is int64_t:
-        nan_val = NPY_NAT
-    elif numeric_t is int32_t:
-        nan_val = util.INT32_MIN
-    elif numeric_t is int16_t:
-        nan_val = util.INT16_MIN
-    elif numeric_t is int8_t:
-        nan_val = util.INT8_MIN
-    elif numeric_t is float64_t or numeric_t is float32_t:
-        nan_val = NAN
-
     N, K = (<object>values).shape
 
     with nogil:
@@ -1442,11 +1431,11 @@ cdef group_min_max(
                         #  we can downcast out if appropriate.
                         out[i, j] = 0
                     elif numeric_t is float32_t or numeric_t is float64_t:
-                        out[i, j] = nan_val
+                        out[i, j] = NAN
                     elif numeric_t is int64_t:
                         # Per above, this is a placeholder in
                         #  non-is_datetimelike cases.
-                        out[i, j] = nan_val
+                        out[i, j] = NPY_NAT
                     else:
                         # placeholder, see above
                         out[i, j] = 0

pandas/_libs/hashing.pyx

@@ -1,8 +1,7 @@
 # Translated from the reference implementation
 # at https://github.com/veorq/SipHash
 
-import cython
-
+cimport cython
 from libc.stdlib cimport (
     free,
     malloc,

pandas/_libs/internals.pyx

@@ -1,9 +1,8 @@
 from collections import defaultdict
 
-import cython
-from cython import Py_ssize_t
-
+cimport cython
 from cpython.slice cimport PySlice_GetIndicesEx
+from cython cimport Py_ssize_t
 
 
 cdef extern from "Python.h":

pandas/_libs/interval.pyx

@@ -11,6 +11,7 @@ from cpython.datetime cimport (
 
 import_datetime()
 
+cimport cython
 from cpython.object cimport (
     Py_EQ,
     Py_GE,
@@ -20,9 +21,8 @@ from cpython.object cimport (
     Py_NE,
     PyObject_RichCompare,
 )
+from cython cimport Py_ssize_t
 
-import cython
-from cython import Py_ssize_t
 import numpy as np
 
 cimport numpy as cnp

pandas/_libs/join.pyx

@@ -1,5 +1,5 @@
-import cython
-from cython import Py_ssize_t
+cimport cython
+from cython cimport Py_ssize_t
 import numpy as np
 
 cimport numpy as cnp
@@ -233,6 +233,8 @@ cdef void _get_result_indexer(intp_t[::1] sorter, intp_t[::1] indexer) nogil:
         indexer[:] = -1
 
 
+@cython.wraparound(False)
+@cython.boundscheck(False)
 def ffill_indexer(const intp_t[:] indexer) -> np.ndarray:
     cdef:
         Py_ssize_t i, n = len(indexer)

pandas/_libs/lib.pyx

@@ -3,9 +3,7 @@ from decimal import Decimal
 from enum import Enum
 import warnings
 
-import cython
-from cython import Py_ssize_t
-
+cimport cython
 from cpython.datetime cimport (
     PyDate_Check,
     PyDateTime_Check,
@@ -25,7 +23,10 @@ from cpython.tuple cimport (
     PyTuple_New,
     PyTuple_SET_ITEM,
 )
-from cython cimport floating
+from cython cimport (
+    Py_ssize_t,
+    floating,
+)
 
 import_datetime()
 

pandas/_libs/missing.pyx

@@ -2,8 +2,8 @@ from decimal import Decimal
 import numbers
 from sys import maxsize
 
-import cython
-from cython import Py_ssize_t
+cimport cython
+from cython cimport Py_ssize_t
 import numpy as np
 
 cimport numpy as cnp

pandas/_libs/ops.pyx

@@ -1,5 +1,6 @@
 import operator
 
+cimport cython
 from cpython.object cimport (
     Py_EQ,
     Py_GE,
@@ -9,9 +10,8 @@ from cpython.object cimport (
     Py_NE,
     PyObject_RichCompareBool,
 )
+from cython cimport Py_ssize_t
 
-import cython
-from cython import Py_ssize_t
 import numpy as np
 
 from numpy cimport (

pandas/_libs/parsers.pyx

@@ -12,16 +12,7 @@ import sys
 import time
 import warnings
 
-from libc.stdlib cimport free
-from libc.string cimport (
-    strcasecmp,
-    strlen,
-    strncpy,
-)
-
-import cython
-from cython import Py_ssize_t
-
+cimport cython
 from cpython.bytes cimport (
     PyBytes_AsString,
     PyBytes_FromString,
@@ -40,6 +31,13 @@ from cpython.unicode cimport (
     PyUnicode_Decode,
     PyUnicode_DecodeUTF8,
 )
+from cython cimport Py_ssize_t
+from libc.stdlib cimport free
+from libc.string cimport (
+    strcasecmp,
+    strlen,
+    strncpy,
+)
 
 
 cdef extern from "Python.h":