Add table format "colon_grid"

tabulate/__init__.py

@@ -134,6 +134,30 @@ def _pipe_line_with_colons(colwidths, colaligns):
     return "|" + "|".join(segments) + "|"
 
 
+def _grid_segment_with_colons(colwidth, align):
+    """Return a segment of a horizontal line with optional colons which indicate
+    column's alignment in a grid table."""
+    width = colwidth
+    if align == "right":
+        return ("=" * (width - 1)) + ":"
+    elif align == "center":
+        return ":" + ("=" * (width - 2)) + ":"
+    elif align == "left":
+        return ":" + ("=" * (width - 1))
+    else:
+        return "=" * width
+
+
+def _grid_line_with_colons(colwidths, colaligns):
+    """Return a horizontal line with optional colons to indicate column's alignment
+    in a grid table."""
+    if not colaligns:
+        colaligns = [""] * len(colwidths)
+    segments = [_grid_segment_with_colons(w, a) for a, w in zip(colaligns, colwidths)]
+    return "+" + "+".join(segments) + "+"
+
+
+
 def _mediawiki_row_with_attrs(separator, cell_values, colwidths, colaligns):
     alignment = {
         "left": "",
@@ -400,6 +424,16 @@ def escape_empty(val):
         padding=1,
         with_header_hide=None,
     ),
+    "colon_grid": TableFormat(
+        lineabove=Line("+", "-", "+", "+"),
+        linebelowheader=_grid_line_with_colons,
+        linebetweenrows=Line("+", "-", "+", "+"),
+        linebelow=Line("+", "-", "+", "+"),
+        headerrow=DataRow("|", "|", "|"),
+        datarow=DataRow("|", "|", "|"),
+        padding=1,
+        with_header_hide=None,
+    ),
     "outline": TableFormat(
         lineabove=Line("+", "-", "+", "+"),
         linebelowheader=Line("+", "=", "+", "+"),
@@ -693,6 +727,7 @@ def escape_empty(val):
     "mixed_grid": "mixed_grid",
     "double_grid": "double_grid",
     "fancy_grid": "fancy_grid",
+    "colon_grid": "colon_grid",
     "pipe": "pipe",
     "orgtbl": "orgtbl",
     "jira": "jira",
@@ -1822,6 +1857,30 @@ def tabulate(
     │ eggs      │  451      │
     ╘═══════════╧═══════════╛
 
+    "colon_grid" is similar to "grid" but uses colons only to define
+    columnwise content alignment, with no whitespace padding:
+
+    >>> print(tabulate([["spam", 41.9999], ["eggs", "451.0"]],
+    ...                ["strings", "numbers"], "colon_grid"))
+    +-----------+-----------+
+    | strings   | numbers   |
+    +:==========+:==========+
+    | spam      | 41.9999   |
+    +-----------+-----------+
+    | eggs      | 451       |
+    +-----------+-----------+
+
+    >>> print(tabulate([["spam", 41.9999], ["eggs", "451.0"]],
+    ...                ["strings", "numbers"], "colon_grid",
+    ...                colalign=["right", "left"]))
+    +-----------+-----------+
+    | strings   | numbers   |
+    +==========:+:==========+
+    | spam      | 41.9999   |
+    +-----------+-----------+
+    | eggs      | 451       |
+    +-----------+-----------+
+
     "outline" is the same as the "grid" format but doesn't draw lines between rows:
 
     >>> print(tabulate([["spam", 41.9999], ["eggs", "451.0"]],
@@ -2138,6 +2197,13 @@ def tabulate(
         numalign = "decimal" if numalign == _DEFAULT_ALIGN else numalign
         stralign = "left" if stralign == _DEFAULT_ALIGN else stralign
 
+    # 'colon_grid' uses colons in the line beneath the header to represent a column's
+    # alignment instead of literally aligning the text differently. Hence,
+    # left alignment of the data in the text output is enforced.
+    if tablefmt == "colon_grid":
+        colglobalalign = "left"
+        headersglobalalign = "left"
+
     # optimization: look for ANSI control codes once,
     # enable smart width functions only if a control code is found
     #
@@ -2206,7 +2272,7 @@ def tabulate(
         aligns = [colglobalalign] * len(cols)
     else: # default
         aligns = [numalign if ct in [int, float] else stralign for ct in coltypes]
-    # then specific alignements
+    # then specific alignments
     if colalign is not None:
         assert isinstance(colalign, Iterable)
         if isinstance(colalign, str):
@@ -2219,9 +2285,14 @@ def tabulate(
     minwidths = (
         [width_fn(h) + min_padding for h in headers] if headers else [0] * len(cols)
     )
+    aligns_copy = aligns.copy()
+    # Reset alignments in copy of alignments list to "left" for 'colon_grid' format,
+    # which enforces left alignment in the text output of the data.
+    if tablefmt == "colon_grid":
+        aligns_copy = ["left"] * len(cols)
     cols = [
         _align_column(c, a, minw, has_invisible, enable_widechars, is_multiline)
-        for c, a, minw in zip(cols, aligns, minwidths)
+        for c, a, minw in zip(cols, aligns_copy, minwidths)
     ]
 
     aligns_headers = None
@@ -2233,7 +2304,7 @@ def tabulate(
             aligns_headers = [headersglobalalign] * len(t_cols)
         else: # default
             aligns_headers = aligns or [stralign] * len(headers)
-        # then specific header alignements
+        # then specific header alignments
         if headersalign is not None:
             assert isinstance(headersalign, Iterable)
             if isinstance(headersalign, str):

test/test_output.py

@@ -1414,6 +1414,97 @@ def test_fancy_grid_multiline_row_align():
     assert_equal(expected, result)
 
 
+def test_colon_grid():
+    "Output: colon_grid with two columns aligned left and center"
+    expected = "\n".join(
+        [
+            "+------+------+",
+            "| H1   | H2   |",
+            "+=====:+:====:+",
+            "| 3    | 4    |",
+            "+------+------+",
+        ]
+    )
+    result = tabulate([[3, 4]], headers=("H1", "H2"), tablefmt="colon_grid", colalign=["right", "center"])
+    assert_equal(expected, result)
+
+
+def test_colon_grid_wide_characters():
+    "Output: colon_grid with wide chars in header"
+    try:
+        import wcwidth  # noqa
+    except ImportError:
+        skip("test_colon_grid_wide_characters is skipped")
+    headers = list(_test_table_headers)
+    headers[1] = "配列"
+    expected = "\n".join(
+        [
+            "+-----------+---------+",
+            "| strings   | 配列    |",
+            "+:==========+========:+",
+            "| spam      | 41.9999 |",
+            "+-----------+---------+",
+            "| eggs      | 451     |",
+            "+-----------+---------+",
+        ]
+    )
+    result = tabulate(_test_table, headers, tablefmt="colon_grid", colalign=["left", "right"])
+    assert_equal(expected, result)
+
+
+def test_colon_grid_headerless():
+    "Output: colon_grid without headers"
+    expected = "\n".join(
+        [
+            "+------+---------+",
+            "| spam | 41.9999 |",
+            "+------+---------+",
+            "| eggs | 451     |",
+            "+------+---------+",
+        ]
+    )
+    result = tabulate(_test_table, tablefmt="colon_grid")
+    assert_equal(expected, result)
+
+
+def test_colon_grid_multiline():
+    "Output: colon_grid with multiline cells"
+    table = [["Data\n5", "33\n3"]]
+    headers = ["H1\n1", "H2\n2"]
+    expected = "\n".join(
+        [
+            "+------+------+",
+            "| H1   | H2   |",
+            "| 1    | 2    |",
+            "+:=====+:=====+",
+            "| Data | 33   |",
+            "| 5    | 3    |",
+            "+------+------+",
+        ]
+    )
+    result = tabulate(table, headers, tablefmt="colon_grid")
+    assert_equal(expected, result)
+
+
+def test_colon_grid_with_empty_cells():
+    table = [["A", ""], ["", "B"]]
+    headers = ["H1", "H2"]
+    alignments = ["center", "right"]
+    expected = "\n".join(
+        [
+            "+------+------+",
+            "| H1   | H2   |",
+            "+:====:+=====:+",
+            "| A    |      |",
+            "+------+------+",
+            "|      | B    |",
+            "+------+------+",
+        ]
+    )
+    result = tabulate(table, headers, tablefmt="colon_grid", colalign=alignments)
+    assert_equal(expected, result)
+
+
 def test_outline():
     "Output: outline with headers"
     expected = "\n".join(