Corrected future warning in solarposition.py (#1256)

* Corrected future warning in solarposition.py

- corrected code to avoid: casting datetime64[ns, Europe/Berlin] values to int64 with .astype(...) is deprecated and will raise in a future version. Use .view(...) instead.

* Update v0.9.0.rst

Author: YoannUniKS

docs/sphinx/source/whatsnew/v0.9.0.rst

@@ -175,6 +175,7 @@ Bug fixes
 * Corrected an error affecting :py:func:`~pvlib.clearsky.detect_clearsky`
   when data time step is not one minute. Error was introduced in v0.8.1.
   (:issue:`1241`, :pull:`1242`)
+* Corrected :py:func:`~pvlib.solarposition.spa_python` to avoid a future warning. (:pull:`1256`)
 
 Testing
 ~~~~~~~
@@ -212,3 +213,4 @@ Contributors
 * Miguel Sánchez de León Peque (:ghuser:`Peque`)
 * Joe Ranalli (:ghuser:`jranalli`)
 * Chas Schweizer (:ghuser:`cpr-chas`)
+* Yoann Louvet (:ghuser:`YoannUniKS`)

pvlib/solarposition.py

@@ -365,7 +365,7 @@ def spa_python(time, latitude, longitude,
         except (TypeError, ValueError):
             time = pd.DatetimeIndex([time, ])
 
-    unixtime = np.array(time.astype(np.int64)/10**9)
+    unixtime = np.array(time.view(np.int64)/10**9)
 
     spa = _spa_python_import(how)