change default encoding for stringtochar/chartostring

Changelog

@@ -1,3 +1,8 @@
+ version 1.7.4.1 (tag v1.7.4.1rel)
+ =================================
+ * Change default encoding for stringtochar/chartostring functions from 'utf-8' to 'utf-8'/'ascii' for dtype.kind='U'/'S'
+   (issue #1464).
+
  version 1.7.4 (tag v1.7.4rel)
  ================================
  * Make sure automatic conversion of character arrays <--> string arrays works for Unicode strings (issue #1440).

docs/index.html

@@ -1226,7 +1226,7 @@ <h2 id="support-for-complex-numbers">Support for complex numbers</h2>
 <h2 class="section-title" id="header-functions">Functions</h2>
 <dl>
 <dt id="netCDF4.chartostring"><code class="name flex">
-<span>def <span class="ident">chartostring</span></span>(<span>b, encoding='utf-8')</span>
+<span>def <span class="ident">chartostring</span></span>(<span>b, encoding=None)</span>
 </code></dt>
 <dd>
 <div class="desc"><p><strong><code>chartostring(b,encoding='utf-8')</code></strong></p>
@@ -1236,8 +1236,8 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 Will be converted to a array of strings, where each string has a fixed
 length of <code>b.shape[-1]</code> characters.</p>
 <p>optional kwarg <code>encoding</code> can be used to specify character encoding (default
-<code>utf-8</code>). If <code>encoding</code> is 'none' or 'bytes', a <code>numpy.string_</code> byte array is
-returned.</p>
+<code>utf-8</code> for dtype=<code>'UN'</code> or <code>ascii</code> for dtype=<code>'SN'</code>). If <code>encoding</code> is 'none' or 'bytes',
+a <code>numpy.string_</code> byte array is returned.</p>
 <p>returns a numpy string array with datatype <code>'UN'</code> (or <code>'SN'</code>) and shape
 <code>b.shape[:-1]</code> where where <code>N=b.shape[-1]</code>.</p></div>
 </dd>
@@ -1254,7 +1254,7 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 <p><strong>calendar</strong>: describes the calendar to be used in the time calculations.
 All the values currently defined in the
 <code>CF metadata convention &lt;http://cfconventions.org/cf-conventions/cf-conventions#calendar&gt;</code>__ are supported.
-Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian'
+Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian', 'tai',
 'noleap', '365_day', '360_day', 'julian', 'all_leap', '366_day'</strong>.
 Default is <code>None</code> which means the calendar associated with the first
 input datetime instance will be used.</p>
@@ -1305,7 +1305,7 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 <p><strong>calendar</strong>: describes the calendar to be used in the time calculations.
 All the values currently defined in the
 <code>CF metadata convention &lt;http://cfconventions.org/cf-conventions/cf-conventions#calendar&gt;</code>__ are supported.
-Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian'
+Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian', 'tai',
 'noleap', '365_day', '360_day', 'julian', 'all_leap', '366_day'</strong>.
 Default is <code>None</code> which means the calendar associated with the first
 input datetime instance will be used.</p>
@@ -1381,7 +1381,7 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 <p><strong>calendar</strong>: describes the calendar used in the time calculations.
 All the values currently defined in the
 <code>CF metadata convention &lt;http://cfconventions.org/cf-conventions/cf-conventions#calendar&gt;</code>__ are supported.
-Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian'
+Valid calendars <strong>'standard', 'gregorian', 'proleptic_gregorian', 'tai',
 'noleap', '365_day', '360_day', 'julian', 'all_leap', '366_day'</strong>.
 Default is <strong>'standard'</strong>, which is a mixed Julian/Gregorian calendar.</p>
 <p><strong>only_use_cftime_datetimes</strong>: if False, python datetime.datetime
@@ -1476,7 +1476,7 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 (default) or <code>'U1'</code> (if dtype=<code>'U'</code>)</p></div>
 </dd>
 <dt id="netCDF4.stringtochar"><code class="name flex">
-<span>def <span class="ident">stringtochar</span></span>(<span>a, encoding='utf-8', n_strlen=None)</span>
+<span>def <span class="ident">stringtochar</span></span>(<span>a, encoding=None, n_strlen=None)</span>
 </code></dt>
 <dd>
 <div class="desc"><p><strong><code>stringtochar(a,encoding='utf-8',n_strlen=None)</code></strong></p>
@@ -1487,8 +1487,8 @@ <h2 class="section-title" id="header-functions">Functions</h2>
 Will be converted to
 an array of characters (datatype <code>'S1'</code> or <code>'U1'</code>) of shape <code>a.shape + (N,)</code>.</p>
 <p>optional kwarg <code>encoding</code> can be used to specify character encoding (default
-<code>utf-8</code>). If <code>encoding</code> is 'none' or 'bytes', a <code>numpy.string_</code> the input array
-is treated a raw byte strings (<code>numpy.string_</code>).</p>
+<code>utf-8</code> for dtype=<code>'UN'</code> or <code>ascii</code> for dtype=<code>'SN'</code>). If <code>encoding</code> is 'none' or 'bytes',
+a <code>numpy.string_</code> the input array is treated a raw byte strings (<code>numpy.string_</code>).</p>
 <p>optional kwarg <code>n_strlen</code> is the number of characters in each string.
 Default
 is None, which means <code>n_strlen</code> will be set to a.itemsize (the number of bytes

examples/tutorial.py

@@ -163,6 +163,7 @@ def walktree(top):
 datac2.imag = datain['imag']
 print(datac.dtype,datac)
 print(datac2.dtype,datac2)
+nc.close()
 
 # more complex compound type example.
 nc = Dataset('compound_example.nc','w') # create a new dataset.

src/netCDF4/__init__.pyi

@@ -704,7 +704,8 @@ def stringtochar(
 @overload
 def stringtochar(
     a: npt.NDArray[np.character],
-    encoding: str = ...,
+    encoding: str | None = None,
+    n_strlen: int | None = None,
 ) -> npt.NDArray[np.str_] | npt.NDArray[np.bytes_]: ...
 @overload
 def chartostring(
@@ -714,7 +715,7 @@ def chartostring(
 @overload
 def chartostring(
     b: npt.NDArray[np.character],
-    encoding: str = ...,
+    encoding: str | None = None,
 ) -> npt.NDArray[np.str_] | npt.NDArray[np.bytes_]: ...
 def getlibversion() -> str: ...
 def rc_get(key: str) -> str | None: ...

src/netCDF4/_netCDF4.pyx

@@ -1,4 +1,4 @@
-"""Version 1.7.4
+"""Version 1.7.4.1
 -------------
 
 # Introduction
@@ -1283,7 +1283,7 @@ import sys
 import functools
 from typing import Union
 
-__version__ = "1.7.4"
+__version__ = "1.7.4.1"
 
 # Initialize numpy
 import posixpath
@@ -6788,7 +6788,7 @@ returns a rank 1 numpy character array of length NUMCHARS with datatype `'S1'`
     arr[0:len(string)] = tuple(string)
     return arr
 
-def stringtochar(a,encoding='utf-8',n_strlen=None):
+def stringtochar(a,encoding=None,n_strlen=None):
     """
 **`stringtochar(a,encoding='utf-8',n_strlen=None)`**
 
@@ -6799,8 +6799,8 @@ is the number of characters in each string.  Will be converted to
 an array of characters (datatype `'S1'` or `'U1'`) of shape `a.shape + (N,)`.
 
 optional kwarg `encoding` can be used to specify character encoding (default
-`utf-8`). If `encoding` is 'none' or 'bytes', a `numpy.string_` the input array
-is treated a raw byte strings (`numpy.string_`).
+`utf-8` for dtype=`'UN'` or `ascii` for dtype=`'SN'`). If `encoding` is 'none' or 'bytes', 
+a `numpy.string_` the input array is treated a raw byte strings (`numpy.string_`).
 
 optional kwarg `n_strlen` is the number of characters in each string.  Default
 is None, which means `n_strlen` will be set to a.itemsize (the number of bytes
@@ -6809,10 +6809,15 @@ used to represent each string in the input array).
 returns a numpy character array with datatype `'S1'` or `'U1'`
 and shape `a.shape + (N,)`, where N is the length of each string in a."""
     dtype = a.dtype.kind
-    if n_strlen is None:
-        n_strlen = a.dtype.itemsize
     if dtype not in ["S","U"]:
         raise ValueError("type must string or unicode ('S' or 'U')")
+    if encoding is None:
+       if dtype == 'S':
+           encoding = 'ascii'
+       else:
+           encoding = 'utf-8'
+    if n_strlen is None:
+        n_strlen = a.dtype.itemsize
     if encoding in ['none','None','bytes']:
         b = numpy.array(tuple(a.tobytes()),'S1')
     elif encoding == 'ascii':
@@ -6827,7 +6832,7 @@ and shape `a.shape + (N,)`, where N is the length of each string in a."""
         b = numpy.array([[bb[i:i+1] for i in range(n_strlen)] for bb in bbytes])
     return b
 
-def chartostring(b,encoding='utf-8'):
+def chartostring(b,encoding=None):
     """
 **`chartostring(b,encoding='utf-8')`**
 
@@ -6838,14 +6843,19 @@ Will be converted to a array of strings, where each string has a fixed
 length of `b.shape[-1]` characters.
 
 optional kwarg `encoding` can be used to specify character encoding (default
-`utf-8`). If `encoding` is 'none' or 'bytes', a `numpy.string_` byte array is
-returned.
+`utf-8` for dtype=`'UN'` or `ascii` for dtype=`'SN'`). If `encoding` is 'none' or 'bytes', 
+a `numpy.string_` byte array is returned.
 
 returns a numpy string array with datatype `'UN'` (or `'SN'`) and shape
 `b.shape[:-1]` where where `N=b.shape[-1]`."""
     dtype = b.dtype.kind
     if dtype not in ["S","U"]:
         raise ValueError("type must be string or unicode ('S' or 'U')")
+    if encoding is None:
+       if dtype == 'S':
+           encoding = 'ascii'
+       else:
+           encoding = 'utf-8'
     bs = b.tobytes()
     slen = int(b.shape[-1])
     if encoding in ['none','None','bytes']: