fractions — 分数

创建有理数实例

# fractions_create_integers.py
import fractions

for n, d in [(1, 2), (2, 4), (3, 6)]:
    f = fractions.Fraction(n, d)
    print('{}/{} = {}'.format(n, d, f))

# fractions_create_strings.py
import fractions

for s in ['1/2', '2/4', '3/6']:
    f = fractions.Fraction(s)
    print('{} = {}'.format(s, f))

# fractions_create_strings_floats.py
import fractions

for s in ['0.5', '1.5', '2.0', '5e-1']:
    f = fractions.Fraction(s)
    print('{0:>4} = {1}'.format(s, f))

# fractions_from_float.py
import fractions

for v in [0.1, 0.5, 1.5, 2.0]:
    print('{} = {}'.format(v, fractions.Fraction(v)))

# fractions_from_decimal.py
import decimal
import fractions

values = [
    decimal.Decimal('0.1'),
    decimal.Decimal('0.5'),
    decimal.Decimal('1.5'),
    decimal.Decimal('2.0'),
]

for v in values:
    print('{} = {}'.format(v, fractions.Fraction(v)))

四则运算

# fractions_arithmetic.py
import fractions

f1 = fractions.Fraction(1, 2)
f2 = fractions.Fraction(3, 4)

print('{} + {} = {}'.format(f1, f2, f1 + f2))
print('{} - {} = {}'.format(f1, f2, f1 - f2))
print('{} * {} = {}'.format(f1, f2, f1 * f2))
print('{} / {} = {}'.format(f1, f2, f1 / f2))

近似值

# fractions_limit_denominator.py
import fractions
import math

print('PI       =', math.pi)

f_pi = fractions.Fraction(str(math.pi))
print('No limit =', f_pi)

for i in [1, 6, 11, 60, 70, 90, 100]:
    limited = f_pi.limit_denominator(i)
    print('{0:8} = {1}'.format(i, limited))