Move pformatters into new `.devx.pformat`

Since `._code` is prolly gonna get renamed (to something "frame & stack
tools" related) and to give a bit better organization.

Also adds a new `add_div()` helper, factored out of ctxc message
creation in `._rpc._invoke()`, for adding a little "header line" divider
under a given `message: str` with a little math to center it.

tractor/devx/pformat.py

@@ -0,0 +1,135 @@
+# tractor: structured concurrent "actors".
+# Copyright 2018-eternity Tyler Goodlet.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+'''
+Pretty formatters for use throughout the code base.
+Mostly handy for logging and exception message content.
+
+'''
+import textwrap
+import traceback
+
+
+def add_div(
+    message: str,
+    div_str: str = '------ - ------',
+
+) -> str:
+    '''
+    Add a "divider string" to the input `message` with
+    a little math to center it underneath.
+
+    '''
+    div_offset: int = (
+        round(len(message)/2)+1
+        -
+        round(len(div_str)/2)+1
+    )
+    div_str: str = (
+        '\n' + ' '*div_offset + f'{div_str}\n'
+    )
+    return div_str
+
+
+def pformat_boxed_tb(
+    tb_str: str,
+    fields_str: str|None = None,
+    field_prefix: str = ' |_',
+
+    tb_box_indent: int|None = None,
+    tb_body_indent: int = 1,
+
+) -> str:
+    '''
+    Create a "boxed" looking traceback string.
+
+    Useful for emphasizing traceback text content as being an
+    embedded attribute of some other object (like
+    a `RemoteActorError` or other boxing remote error shuttle
+    container).
+
+    Any other parent/container "fields" can be passed in the
+    `fields_str` input along with other prefix/indent settings.
+
+    '''
+    if (
+        fields_str
+        and
+        field_prefix
+    ):
+        fields: str = textwrap.indent(
+            fields_str,
+            prefix=field_prefix,
+        )
+    else:
+        fields = fields_str or ''
+
+    tb_body = tb_str
+    if tb_body_indent:
+        tb_body: str = textwrap.indent(
+            tb_str,
+            prefix=tb_body_indent * ' ',
+        )
+
+    tb_box: str = (
+        f'|\n'
+        f' ------ - ------\n'
+        f'{tb_body}'
+        f' ------ - ------\n'
+        f'_|\n'
+    )
+    tb_box_indent: str = (
+        tb_box_indent
+        or
+        1
+
+        # (len(field_prefix))
+        # ? ^-TODO-^ ? if you wanted another indent level
+    )
+    if tb_box_indent > 0:
+        tb_box: str = textwrap.indent(
+            tb_box,
+            prefix=tb_box_indent * ' ',
+        )
+
+    return (
+        fields
+        +
+        tb_box
+    )
+
+
+def pformat_caller_frame(
+    stack_limit: int = 1,
+    box_tb: bool = True,
+) -> str:
+    '''
+    Capture and return the traceback text content from
+    `stack_limit` call frames up.
+
+    '''
+    tb_str: str = (
+        '\n'.join(
+            traceback.format_stack(limit=stack_limit)
+        )
+    )
+    if box_tb:
+        tb_str: str = pformat_boxed_tb(
+            tb_str=tb_str,
+            field_prefix='  ',
+            indent='',
+        )
+    return tb_str