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Improve tests for str to Fraction conversion by serhiy-storchaka · Pull Request #134010 · python/cpython · GitHub

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Improve tests for str to Fraction conversion #134010

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serhiy-storchaka merged 1 commit into from
May 14, 2025
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Improve tests for str to Fraction conversion #134010

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207 changes: 97 additions & 110 deletions Lib/test/test_fractions.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
"""Tests for Lib/fractions.py."""

from decimal import Decimal
from test.support import requires_IEEE_754
from test.support import requires_IEEE_754, adjust_int_max_str_digits
import math
import numbers
import operator
Expand Down Expand Up @@ -395,12 +395,14 @@ class B(metaclass=M):

def testFromString(self):
self.assertEqual((5, 1), _components(F("5")))
self.assertEqual((5, 1), _components(F("005")))
self.assertEqual((3, 2), _components(F("3/2")))
self.assertEqual((3, 2), _components(F("3 / 2")))
self.assertEqual((3, 2), _components(F(" \n +3/2")))
self.assertEqual((-3, 2), _components(F("-3/2 ")))
self.assertEqual((13, 2), _components(F(" 013/02 \n ")))
self.assertEqual((13, 2), _components(F(" 0013/002 \n ")))

skirpichev May 14, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Why this was replaced, not added?

serhiy-storchaka May 14, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

It is virtually the same test, but tests that more than one zero is accepted. There were no tests for leading zero in other forms, so they were added.
self.assertEqual((16, 5), _components(F(" 3.2 ")))
self.assertEqual((16, 5), _components(F("003.2")))
self.assertEqual((-16, 5), _components(F(" -3.2 ")))
self.assertEqual((-3, 1), _components(F(" -3. ")))
self.assertEqual((3, 5), _components(F(" .6 ")))
Expand All @@ -419,116 +421,101 @@ def testFromString(self):
self.assertRaisesMessage(
ZeroDivisionError, "Fraction(3, 0)",
F, "3/0")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '3/'",
F, "3/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '/2'",
F, "/2")
self.assertRaisesMessage(
# Denominators don't need a sign.
ValueError, "Invalid literal for Fraction: '3/+2'",
F, "3/+2")
self.assertRaisesMessage(
# Imitate float's parsing.
ValueError, "Invalid literal for Fraction: '+ 3/2'",
F, "+ 3/2")
self.assertRaisesMessage(
# Avoid treating '.' as a regex special character.
ValueError, "Invalid literal for Fraction: '3a2'",
F, "3a2")
self.assertRaisesMessage(
# Don't accept combinations of decimals and rationals.
ValueError, "Invalid literal for Fraction: '3/7.2'",
F, "3/7.2")
self.assertRaisesMessage(
# Don't accept combinations of decimals and rationals.
ValueError, "Invalid literal for Fraction: '3.2/7'",
F, "3.2/7")
self.assertRaisesMessage(
# Allow 3. and .3, but not .
ValueError, "Invalid literal for Fraction: '.'",
F, ".")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_'",
F, "_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_1'",
F, "_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1__2'",
F, "1__2")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '/_'",
F, "/_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1_/'",
F, "1_/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '_1/'",
F, "_1/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1__2/'",
F, "1__2/")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/_'",
F, "1/_")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/_1'",
F, "1/_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/1__2'",
F, "1/1__2")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1._111'",
F, "1._111")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1__1'",
F, "1.1__1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1e+_1'",
F, "1.1e+_1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1e+1__1'",
F, "1.1e+1__1")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '123.dd'",
F, "123.dd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '123.5_dd'",
F, "123.5_dd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: 'dd.5'",
F, "dd.5")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '7_dd'",
F, "7_dd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/dd'",
F, "1/dd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/123_dd'",
F, "1/123_dd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '789edd'",
F, "789edd")
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '789e2_dd'",
F, "789e2_dd")

def check_invalid(s):
msg = "Invalid literal for Fraction: " + repr(s)
self.assertRaisesMessage(ValueError, msg, F, s)
Comment on lines +425 to +427

skirpichev May 14, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

This looks fine.

But maybe use subTest?

for value in ["3/", "/2",  # there can be a lot of...
              # Denominators don't need a sign.
              "3/+2", "3/-2",
              # Imitate float's parsing.
              ...]:
    with self.subTest(value=value):
        check_invalid(value)

serhiy-storchaka May 14, 2025

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

The main reason is that if we make error messages more specific, it is easier to add an optional parameter, while keeping default for most tests. For example, I originally planned to add the tests here that are currently in test_limit_int.

check_invalid("3/")
check_invalid("/2")
# Denominators don't need a sign.
check_invalid("3/+2")
check_invalid("3/-2")
# Imitate float's parsing.
check_invalid("+ 3/2")
check_invalid("- 3/2")
# Avoid treating '.' as a regex special character.
check_invalid("3a2")
# Don't accept combinations of decimals and rationals.
check_invalid("3/7.2")
check_invalid("3.2/7")
# No space around dot.
check_invalid("3 .2")
check_invalid("3. 2")
# No space around e.
check_invalid("3.2 e1")
check_invalid("3.2e 1")
# Fractional part don't need a sign.
check_invalid("3.+2")
check_invalid("3.-2")
# Only accept base 10.
check_invalid("0x10")
check_invalid("0x10/1")
check_invalid("1/0x10")
check_invalid("0x10.")
check_invalid("0x10.1")
check_invalid("1.0x10")
check_invalid("1.0e0x10")
# Only accept decimal digits.
check_invalid("³")
check_invalid("³/2")
check_invalid("3/²")
check_invalid("³.2")
check_invalid("3.²")
check_invalid("3.2e²")
check_invalid("¼")
# Allow 3. and .3, but not .
check_invalid(".")
check_invalid("_")
check_invalid("_1")
check_invalid("1__2")
check_invalid("/_")
check_invalid("1_/")
check_invalid("_1/")
check_invalid("1__2/")
check_invalid("1/_")
check_invalid("1/_1")
check_invalid("1/1__2")
check_invalid("1._111")
check_invalid("1.1__1")
check_invalid("1.1e+_1")
check_invalid("1.1e+1__1")
check_invalid("123.dd")
check_invalid("123.5_dd")
check_invalid("dd.5")
check_invalid("7_dd")
check_invalid("1/dd")
check_invalid("1/123_dd")
check_invalid("789edd")
check_invalid("789e2_dd")
# Test catastrophic backtracking.
val = "9"*50 + "_"
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '" + val + "'",
F, val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1/" + val + "'",
F, "1/" + val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1." + val + "'",
F, "1." + val)
self.assertRaisesMessage(
ValueError, "Invalid literal for Fraction: '1.1+e" + val + "'",
F, "1.1+e" + val)
check_invalid(val)
check_invalid("1/" + val)
check_invalid("1." + val)
check_invalid("." + val)
check_invalid("1.1+e" + val)
check_invalid("1.1e" + val)

def test_limit_int(self):
maxdigits = 5000
with adjust_int_max_str_digits(maxdigits):
val = '1' * maxdigits
num = (10**maxdigits - 1)//9
self.assertEqual((num, 1), _components(F(val)))
self.assertRaises(ValueError, F, val + '1')
self.assertEqual((num, 2), _components(F(val + '/2')))
self.assertRaises(ValueError, F, val + '1/2')
self.assertEqual((1, num), _components(F('1/' + val)))
self.assertRaises(ValueError, F, '1/1' + val)
self.assertEqual(((10**(maxdigits+1) - 1)//9, 10**maxdigits),
_components(F('1.' + val)))
self.assertRaises(ValueError, F, '1.1' + val)
self.assertEqual((num, 10**maxdigits), _components(F('.' + val)))
self.assertRaises(ValueError, F, '.1' + val)
self.assertRaises(ValueError, F, '1.1e1' + val)
self.assertEqual((11, 10), _components(F('1.1e' + '0' * maxdigits)))
self.assertRaises(ValueError, F, '1.1e' + '0' * (maxdigits+1))

def testImmutable(self):
r = F(7, 3)
Expand Down
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