Support better type deduction

o Empty/None values are ignored for deducing the type of a column
o Comma-separated numbers are allowed in for int and float types

tabulate/__init__.py

@@ -933,8 +933,13 @@ def _isbool(string):
 def _type(string, has_invisible=True, numparse=True):
     """The least generic type (type(None), int, float, str, unicode).
 
+    Treats empty string as missing for the purposes of type deduction, so as to not influence
+    the type of an otherwise complete column; does *not* result in missingval replacement!
+
     >>> _type(None) is type(None)
     True
+    >>> _type("") is type(None)
+    True
     >>> _type("foo") is type("")
     True
     >>> _type("1") is type(1)
@@ -949,15 +954,26 @@ def _type(string, has_invisible=True, numparse=True):
     if has_invisible and isinstance(string, (str, bytes)):
         string = _strip_ansi(string)
 
-    if string is None:
+    if string is None or (isinstance(string, (bytes, str)) and not string):
         return type(None)
     elif hasattr(string, "isoformat"):  # datetime.datetime, date, and time
         return str
     elif _isbool(string):
         return bool
-    elif _isint(string) and numparse:
+    elif numparse and (
+        _isint(string) or (
+            isinstance(string, str)
+            and _isnumber_with_thousands_separator(string)
+            and '.' not in string 
+        )
+    ):
         return int
-    elif _isnumber(string) and numparse:
+    elif numparse and (
+        _isnumber(string) or (
+            isinstance(string, str)
+            and _isnumber_with_thousands_separator(string)
+        )
+    ):
         return float
     elif isinstance(string, bytes):
         return bytes
@@ -1251,7 +1267,7 @@ def _column_type(strings, has_invisible=True, numparse=True):
 
 
 def _format(val, valtype, floatfmt, intfmt, missingval="", has_invisible=True):
-    """Format a value according to its type.
+    """Format a value according to its deduced type.  Empty values are deemed valid for any type.
 
     Unicode is supported:
 
@@ -1264,6 +1280,8 @@ def _format(val, valtype, floatfmt, intfmt, missingval="", has_invisible=True):
     """  # noqa
     if val is None:
         return missingval
+    if isinstance(val, (bytes, str)) and not val:
+        return ""
 
     if valtype is str:
         return f"{val}"
@@ -1298,6 +1316,8 @@ def _format(val, valtype, floatfmt, intfmt, missingval="", has_invisible=True):
             formatted_val = format(float(raw_val), floatfmt)
             return val.replace(raw_val, formatted_val)
         else:
+            if isinstance(val,str) and ',' in val:
+                val = val.replace(',', '')  # handle thousands-separators
             return format(float(val), floatfmt)
     else:
         return f"{val}"
@@ -1592,9 +1612,10 @@ def _wrap_text_to_colwidths(list_of_lists, colwidths, numparses=True):
 
             if width is not None:
                 wrapper = _CustomTextWrap(width=width)
-                # Cast based on our internal type handling
-                # Any future custom formatting of types (such as datetimes)
-                # may need to be more explicit than just `str` of the object
+                # Cast based on our internal type handling. Any future custom
+                # formatting of types (such as datetimes) may need to be more
+                # explicit than just `str` of the object. Also doesn't work for
+                # custom floatfmt/intfmt, nor with any missing/blank cells.
                 casted_cell = (
                     str(cell) if _isnumber(cell) else _type(cell, numparse)(cell)
                 )

test/test_output.py

@@ -2824,6 +2824,13 @@ def test_floatfmt():
     assert_equal(expected, result)
 
 
+def test_floatfmt_thousands():
+    "Output: floating point format"
+    result = tabulate([["1.23456789"], [1.0], ["1,234.56"]], floatfmt=".3f", tablefmt="plain")
+    expected = "   1.235\n   1.000\n1234.560"
+    assert_equal(expected, result)
+
+
 def test_floatfmt_multi():
     "Output: floating point format different for each column"
     result = tabulate(
@@ -2964,6 +2971,32 @@ def test_missingval_multi():
     assert_equal(expected, result)
 
 
+def test_column_emptymissing_deduction():
+    "Missing or empty/blank values shouldn't change type deduction of rest of column"
+    from fractions import Fraction
+
+    test_table = [
+        [None, "1.23423515351", Fraction(1, 3)],
+        [Fraction(56789, 1000000), 12345.1, b"abc"],
+        ["", b"", None],
+        [Fraction(10000, 3), None, ""],
+    ]
+    result = tabulate(
+        test_table,
+        floatfmt=",.5g",
+        missingval="?",
+    )
+    print(f"\n{result}")
+    expected = """\
+------------  -----------  ---
+    ?              1.2342  1/3
+    0.056789  12,345       abc
+                           ?
+3,333.3            ?
+------------  -----------  ---"""
+    assert_equal(expected, result)
+
+
 def test_column_alignment():
     "Output: custom alignment for text and numbers"
     expected = "\n".join(["-----  ---", "Alice   1", "  Bob  333", "-----  ---"])