Better magic underscore errors

See #2072

Author: nicholas-esterer

.gitignore

@@ -31,7 +31,7 @@ node_modules/
 
 # virtual envs
 vv
-venv
+venv*
 
 # dist files
 build

packages/python/plotly/_plotly_utils/exceptions.py

@@ -83,3 +83,14 @@ def __init__(self, obj, path, notes=()):
         super(PlotlyDataTypeError, self).__init__(
             message=message, path=path, notes=notes
         )
+
+
+class PlotlyKeyError(LookupError):
+    """
+    KeyErrors are not printed as beautifully as other errors (this is so that
+    {}[''] prints    "KeyError: ''" and not "KeyError:"). So here we subclass
+    LookupError to make a PlotlyKeyError object which will print nicer error
+    messages for KeyErrors.
+    """
+
+    pass

packages/python/plotly/_plotly_utils/utils.py

@@ -2,6 +2,7 @@
 import json as _json
 import sys
 import re
+from functools import reduce
 
 from _plotly_utils.optional_imports import get_module
 from _plotly_utils.basevalidators import ImageUriValidator
@@ -10,6 +11,20 @@
 PY36_OR_LATER = sys.version_info >= (3, 6)
 
 
+def cumsum(x):
+    """
+    Custom cumsum to avoid a numpy import.
+    """
+
+    def _reducer(a, x):
+        if len(a) == 0:
+            return [x]
+        return a + [a[-1] + x]
+
+    ret = reduce(_reducer, x, [])
+    return ret
+
+
 class PlotlyJSONEncoder(_json.JSONEncoder):
     """
     Meant to be passed as the `cls` kwarg to json.dumps(obj, cls=..)
@@ -256,3 +271,76 @@ def _get_int_type():
     else:
         int_type = (int,)
     return int_type
+
+
+def split_multichar(ss, chars):
+    """
+    Split all the strings in ss at any of the characters in chars.
+    Example:
+
+        >>> ss = ["a.string[0].with_separators"]
+        >>> chars = list(".[]_")
+        >>> split_multichar(ss, chars)
+        ['a', 'string', '0', '', 'with', 'separators']
+
+    :param (list) ss: A list of strings.
+    :param (list) chars: Is a list of chars (note: not a string).
+    """
+    if len(chars) == 0:
+        return ss
+    c = chars.pop()
+    ss = reduce(lambda x, y: x + y, map(lambda x: x.split(c), ss))
+    return split_multichar(ss, chars)
+
+
+def split_string_positions(ss):
+    """
+    Given a list of strings split using split_multichar, return a list of
+    integers representing the indices of the first character of every string in
+    the original string.
+    Example:
+
+        >>> ss = ["a.string[0].with_separators"]
+        >>> chars = list(".[]_")
+        >>> ss_split = split_multichar(ss, chars)
+        >>> ss_split
+        ['a', 'string', '0', '', 'with', 'separators']
+        >>> split_string_positions(ss_split)
+        [0, 2, 9, 11, 12, 17]
+
+    :param (list) ss: A list of strings.
+    """
+    return list(
+        map(
+            lambda t: t[0] + t[1],
+            zip(range(len(ss)), cumsum([0] + list(map(len, ss[:-1])))),
+        )
+    )
+
+
+def display_string_positions(p, i=None):
+    """
+    Return a string that is whitespace except at p[i] which is replaced with ^.
+    If i is None then all the indices of the string in p are replaced with ^.
+    Example:
+
+        >>> ss = ["a.string[0].with_separators"]
+        >>> chars = list(".[]_")
+        >>> ss_split = split_multichar(ss, chars)
+        >>> ss_split
+        ['a', 'string', '0', '', 'with', 'separators']
+        >>> ss_pos = split_string_positions(ss_split)
+        >>> ss[0]
+        'a.string[0].with_separators'
+        >>> display_string_positions(ss_pos,4)
+        '            ^'
+    :param (list) p: A list of integers.
+    :param (integer|None) i: Optional index of p to display.
+    """
+    s = [" " for _ in range(max(p) + 1)]
+    if i is None:
+        for p_ in p:
+            s[p_] = "^"
+    else:
+        s[p[i]] = "^"
+    return "".join(s)