From 171d507b6711da4e62c1ec5b5743e122fd0029bc Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Thu, 28 May 2020 15:32:53 -0700
Subject: [PATCH] CLN: simplify to_offset

---
 pandas/_libs/tslibs/offsets.pyx               | 32 +++----------------
 .../tseries/frequencies/test_to_offset.py     | 10 +-----
 2 files changed, 6 insertions(+), 36 deletions(-)

diff --git a/pandas/_libs/tslibs/offsets.pyx b/pandas/_libs/tslibs/offsets.pyx
index 30a1490fdf862..855fc014bfe7e 100644
--- a/pandas/_libs/tslibs/offsets.pyx
+++ b/pandas/_libs/tslibs/offsets.pyx
@@ -3532,16 +3532,6 @@ prefix_mapping = {
     ]
 }
 
-_name_to_offset_map = {
-    "days": Day(1),
-    "hours": Hour(1),
-    "minutes": Minute(1),
-    "seconds": Second(1),
-    "milliseconds": Milli(1),
-    "microseconds": Micro(1),
-    "nanoseconds": Nano(1),
-}
-
 # hack to handle WOM-1MON
 opattern = re.compile(
     r"([+\-]?\d*|[+\-]?\d*\.\d*)\s*([A-Za-z]+([\-][\dA-Za-z\-]+)?)"
@@ -3695,26 +3685,12 @@ cpdef to_offset(freq):
         delta = _get_offset(name) * stride
 
     elif isinstance(freq, timedelta):
-        from .timedeltas import Timedelta
-
-        delta = None
-        freq = Timedelta(freq)
-        try:
-            for name in freq.components._fields:
-                offset = _name_to_offset_map[name]
-                stride = getattr(freq.components, name)
-                if stride != 0:
-                    offset = stride * offset
-                    if delta is None:
-                        delta = offset
-                    else:
-                        delta = delta + offset
-        except ValueError as err:
-            raise ValueError(INVALID_FREQ_ERR_MSG.format(freq)) from err
+        return delta_to_tick(freq)
 
-    else:
+    elif isinstance(freq, str):
         delta = None
         stride_sign = None
+
         try:
             split = re.split(opattern, freq)
             if split[-1] != "" and not split[-1].isspace():
@@ -3744,6 +3720,8 @@ cpdef to_offset(freq):
                     delta = delta + offset
         except (ValueError, TypeError) as err:
             raise ValueError(INVALID_FREQ_ERR_MSG.format(freq)) from err
+    else:
+        delta = None
 
     if delta is None:
         raise ValueError(INVALID_FREQ_ERR_MSG.format(freq))
diff --git a/pandas/tests/tseries/frequencies/test_to_offset.py b/pandas/tests/tseries/frequencies/test_to_offset.py
index beaefe9109e91..d3510eaa5c749 100644
--- a/pandas/tests/tseries/frequencies/test_to_offset.py
+++ b/pandas/tests/tseries/frequencies/test_to_offset.py
@@ -137,6 +137,7 @@ def test_to_offset_leading_plus(freqstr, expected):
         (dict(hours=1), offsets.Hour(1)),
         (dict(hours=1), frequencies.to_offset("60min")),
         (dict(microseconds=1), offsets.Micro(1)),
+        (dict(microseconds=0), offsets.Nano(0)),
     ],
 )
 def test_to_offset_pd_timedelta(kwargs, expected):
@@ -146,15 +147,6 @@ def test_to_offset_pd_timedelta(kwargs, expected):
     assert result == expected
 
 
-def test_to_offset_pd_timedelta_invalid():
-    # see gh-9064
-    msg = "Invalid frequency: 0 days 00:00:00"
-    td = Timedelta(microseconds=0)
-
-    with pytest.raises(ValueError, match=msg):
-        frequencies.to_offset(td)
-
-
 @pytest.mark.parametrize(
     "shortcut,expected",
     [