numpy · charris · Sep 11, 2018 · Feb 15, 2018 · mattip · Aug 19, 2018
diff --git a/numpy/core/_dtype.py b/numpy/core/_dtype.py
@@ -0,0 +1,294 @@
+"""
+A place for code to be called from the implementation of np.dtype
+
+String handling is much easier to do correctly in python.
+"""
+from __future__ import division, absolute_import, print_function
+
+import numpy as np
+
+
+def __str__(dtype):
+    if dtype.fields is not None:
+        return _struct_str(dtype, include_align=True)
+    elif dtype.subdtype:
+        return _subarray_str(dtype)
+    elif issubclass(dtype.type, np.flexible) or not dtype.isnative:
+        return dtype.str
+    else:
+        return dtype.name
+
+
+def __repr__(dtype):
+    if dtype.fields is not None:
+        return _struct_repr(dtype)
+    else:
+        return "dtype({})".format(_construction_repr(dtype, include_align=True))
+
+
+def _unpack_field(dtype, offset, title=None):
+    """
+    Helper function to normalize the items in dtype.fields.
+
+    Call as:
+
+    dtype, offset, title = _unpack_field(*dtype.fields[name])
+    """
+    return dtype, offset, title
+
+
+def _isunsized(dtype):
+    # PyDataType_ISUNSIZED
+    return dtype.itemsize == 0
+
+
+def _construction_repr(dtype, include_align=False, short=False):
+    """
+    Creates a string repr of the dtype, excluding the 'dtype()' part
+    surrounding the object. This object may be a string, a list, or
+    a dict depending on the nature of the dtype. This
+    is the object passed as the first parameter to the dtype
+    constructor, and if no additional constructor parameters are
+    given, will reproduce the exact memory layout.
+
+    Parameters
+    ----------
+    short : bool
+        If true, this creates a shorter repr using 'kind' and 'itemsize', instead
+        of the longer type name.
+
+    include_align : bool
+        If true, this includes the 'align=True' parameter
+        inside the struct dtype construction dict when needed. Use this flag
+        if you want a proper repr string without the 'dtype()' part around it.
+
+        If false, this does not preserve the
+        'align=True' parameter or sticky NPY_ALIGNED_STRUCT flag for
+        struct arrays like the regular repr does, because the 'align'
+        flag is not part of first dtype constructor parameter. This
+        mode is intended for a full 'repr', where the 'align=True' is
+        provided as the second parameter.
+    """
+    if dtype.fields is not None:
+        return _struct_str(dtype, include_align=include_align)
+    elif dtype.subdtype:
+        return _subarray_str(dtype)
+
+
+    byteorder = _byte_order_str(dtype)
+
+    if dtype.type == np.bool_:
+        if short:
+            return "'?'"
+        else:
+            return "'bool'"
+
+    elif dtype.type == np.object_:
+        # The object reference may be different sizes on different
+        # platforms, so it should never include the itemsize here.
+        return "'O'"
+
+    elif dtype.type == np.string_:
+        if _isunsized(dtype):
+            return "'S'"
+        else:
+            return "'S%d'" % dtype.itemsize
+
+    elif dtype.type == np.unicode_:
+        if _isunsized(dtype):
+            return "'%sU'" % byteorder
+        else:
+            return "'%sU%d'" % (byteorder, dtype.itemsize / 4)
+
+    elif dtype.type == np.void:
+        if _isunsized(dtype):
+            return "'V'"
+        else:
+            return "'V%d'" % dtype.itemsize
+
+    elif dtype.type == np.datetime64:
+        return "'%sM8%s'" % (byteorder, _datetime_metadata_str(dtype))
+
+    elif dtype.type == np.timedelta64:
+        return "'%sm8%s'" % (byteorder, _datetime_metadata_str(dtype))
+
+    elif np.issubdtype(dtype, np.number):
+        # Short repr with endianness, like '<f8'
+        if short or dtype.byteorder not in ('=', '|'):
+            return "'%s%c%d'" % (byteorder, dtype.kind, dtype.itemsize)
+
+        # Longer repr, like 'float64'
+        else:
+            kindstrs = {
+                'u': "uint",
+                'i': "int",
+                'f': "float",
+                'c': "complex"
+            }
+            try:
+                kindstr = kindstrs[dtype.kind]
+            except KeyError:
+                raise RuntimeError(
+                    "internal dtype repr error, unknown kind {!r}"
+                    .format(dtype.kind)
+                )
+            return "'%s%d'" % (kindstr, 8*dtype.itemsize)
+
+    elif dtype.isbuiltin == 2:
+        return dtype.type.__name__
+
+    else:
+        raise RuntimeError(
+            "Internal error: NumPy dtype unrecognized type number")
+
+
+def _byte_order_str(dtype):
+    """ Normalize byteorder to '<' or '>' """
+    # hack to obtain the native and swapped byte order characters
+    swapped = np.dtype(int).newbyteorder('s')
+    native = swapped.newbyteorder('s')
+
+    byteorder = dtype.byteorder
+    if byteorder == '=':
+        return native.byteorder
+    if byteorder == 's':
+        # TODO: this path can never be reached
+        return swapped.byteorder
+    elif byteorder == '|':
+        return ''
+    else:
+        return byteorder
+
+
+def _datetime_metadata_str(dtype):
+    # This is a hack since the data is not exposed to python in any other way
+    return dtype.name[dtype.name.rfind('['):]
+
+
+def _struct_dict_str(dtype, includealignedflag):
+    # unpack the fields dictionary into ls
+    names = dtype.names
+    fld_dtypes = []
+    offsets = []
+    titles = []
+    for name in names:
+        fld_dtype, offset, title = _unpack_field(*dtype.fields[name])
+        fld_dtypes.append(fld_dtype)
+        offsets.append(offset)
+        titles.append(title)
+
+    # Build up a string to make the dictionary
+
+    # First, the names
+    ret = "{'names':["
+    ret += ",".join(repr(name) for name in names)
+
+    # Second, the formats
+    ret += "], 'formats':["
+    ret += ",".join(
+        _construction_repr(fld_dtype, short=True) for fld_dtype in fld_dtypes)
+
+    # Third, the offsets
+    ret += "], 'offsets':["
+    ret += ",".join("%d" % offset for offset in offsets)
+
+    # Fourth, the titles
+    if any(title is not None for title in titles):
+        ret += "], 'titles':["
+        ret += ",".join(repr(title) for title in titles)
+
+    # Fifth, the itemsize
+    ret += "], 'itemsize':%d" % dtype.itemsize
+
+    if (includealignedflag and dtype.isalignedstruct):
+        # Finally, the aligned flag
+        ret += ", 'aligned':True}"
+    else:
+        ret += "}"
+
+    return ret
+
+
+def _is_packed(dtype):
+    """
+    Checks whether the structured data type in 'dtype'
+    has a simple layout, where all the fields are in order,
+    and follow each other with no alignment padding.
+
+    When this returns true, the dtype can be reconstructed
+    from a list of the field names and dtypes with no additional
+    dtype parameters.
+
+    Duplicates the C `is_dtype_struct_simple_unaligned_layout` functio.
+    """
+    total_offset = 0
+    for name in dtype.names:
+        fld_dtype, fld_offset, title = _unpack_field(*dtype.fields[name])
+        if fld_offset != total_offset:
+            return False
+        total_offset += fld_dtype.itemsize
+    if total_offset != dtype.itemsize:
+        return False
+    return True
+
+
+def _struct_list_str(dtype):
+    items = []
+    for name in dtype.names:
+        fld_dtype, fld_offset, title = _unpack_field(*dtype.fields[name])
+
+        item = "("
+        if title is not None:
+            item += "({!r}, {!r}), ".format(title, name)
+        else:
+            item += "{!r}, ".format(name)
+        # Special case subarray handling here
+        if fld_dtype.subdtype is not None:
+            base, shape = fld_dtype.subdtype
+            item += "{}, {}".format(
+                _construction_repr(base, short=True),
+                shape
+            )
+        else:
+            item += _construction_repr(fld_dtype, short=True)
+
+        item += ")"
+        items.append(item)
+
+    return "[" + ", ".join(items) + "]"
+
+
+def _struct_str(dtype, include_align):
+    # The list str representation can't include the 'align=' flag,
+    # so if it is requested and the struct has the aligned flag set,
+    # we must use the dict str instead.
+    if not (include_align and dtype.isalignedstruct) and _is_packed(dtype):
+        sub = _struct_list_str(dtype)
+
+    else:
+        sub = _struct_dict_str(dtype, include_align)
+
+    # If the data type isn't the default, void, show it
+    if dtype.type != np.void:
+        return "({t.__module__}.{t.__name__}, {f})".format(t=dtype.type, f=sub)
+    else:
+        return sub
+
+
+def _subarray_str(dtype):
+    base, shape = dtype.subdtype
+    return "({}, {})".format(
+        _construction_repr(base, short=True),
+        shape
+    )
+
+
+def _struct_repr(dtype):
+    s = "dtype("
+    s += _struct_str(dtype, include_align=False)
+    if dtype.isalignedstruct:
+        s += ", align=True"
+    s += ")"
+    return s
+
+