Set date_format to ISO8601 to silence pandas 2.0 UserWarning on read_csv

.github/workflows/ci_tests_legacy.yaml

@@ -67,7 +67,7 @@ jobs:
             python=3.9
             gmt=${{ matrix.gmt_version }}
             numpy
-            pandas
+            pandas<2
             xarray
             netCDF4
             packaging

pygmt/src/x2sys_cross.py

@@ -6,6 +6,7 @@
 from pathlib import Path
 
 import pandas as pd
+from packaging.version import Version
 from pygmt.clib import Session
 from pygmt.exceptions import GMTInvalidInput
 from pygmt.helpers import (
@@ -47,7 +48,7 @@ def tempfile_from_dftrack(track, suffix):
             sep="\t",
             index=False,
             na_rep="NaN",  # write a NaN value explicitly instead of a blank string
-            date_format="%Y-%m-%dT%H:%M:%S.%fZ",
+            date_format="%Y-%m-%dT%H:%M:%S.%fZ",  # ISO8601 format
         )
         yield tmpfilename
     finally:
@@ -229,12 +230,18 @@ def x2sys_cross(tracks=None, outfile=None, **kwargs):
             # Read temporary csv output to a pandas table
             if outfile == tmpfile.name:  # if outfile isn't set, return pd.DataFrame
                 # Read the tab-separated ASCII table
+                date_format_kwarg = (
+                    {"date_format": "ISO8601"}
+                    if Version(pd.__version__) >= Version("2.0.0")
+                    else {}
+                )
                 table = pd.read_csv(
                     tmpfile.name,
                     sep="\t",
                     header=2,  # Column names are on 2nd row
                     comment=">",  # Skip the 3rd row with a ">"
                     parse_dates=[2, 3],  # Datetimes on 3rd and 4th column
+                    **date_format_kwarg,  # Parse dates in ISO8601 format on pandas>=2
                 )
                 # Remove the "# " from "# x" in the first column
                 table = table.rename(columns={table.columns[0]: table.columns[0][2:]})

pygmt/tests/test_x2sys_cross.py

@@ -112,7 +112,7 @@ def test_x2sys_cross_input_two_dataframes(mock_x2sys_home):
         for i in range(2):
             np.random.seed(seed=i)
             track = pd.DataFrame(data=np.random.rand(10, 3), columns=("x", "y", "z"))
-            track["time"] = pd.date_range(start=f"2020-{i}1-01", periods=10, freq="ms")
+            track["time"] = pd.date_range(start=f"2020-{i}1-01", periods=10, freq="min")
             tracks.append(track)
 
         output = x2sys_cross(tracks=tracks, tag=tag, coe="e")