Question

有谁能告诉我为什么超过27位小数会导致TypeError？我查看了官方文档，但没有看到答案。错误消息提到浮动，但我没有在代码中看到任何浮动。我特意摆脱了所有花车。

Evaluate number e to n significant digits (up to 27): 28
Traceback (most recent call last):
  File "ex6.py", line 20, in <module>
    while (deci.Decimal(1) / deci.Decimal((math.factorial(step)))) >     deci.Decimal(eval(sigdig2)):
  File "<string>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'Decimal' and 'float'

＆GT;

# imports necessary modules

import math
import decimal as deci

# defines variables

eul = 0
step = 0

# queries for input

sigdig = int(raw_input("Evaluate number e to n significant digits (up to 27): "))
sigdig2 = 'deci.Decimal(1)/' + str(deci.Decimal(10) ** deci.Decimal(sigdig))

deci.getcontext().prec = (sigdig + 1)

# evaluates e

while (deci.Decimal(1) / deci.Decimal((math.factorial(step)))) > deci.Decimal(eval(sigdig2)):
    eul += (deci.Decimal(1) / deci.Decimal((math.factorial(step))))
    step +=1

#prints the result

print
printer = '"e = %.' + str(sigdig) + 'f" % (eul)'
print eval(printer)

Answer 1

>>> str(decimal.Decimal(10) ** 28)
'1.000000000000000000000000000E+28'  # <- not a decimal
>>> str(decimal.Decimal(10) ** 27)
'1000000000000000000000000000'     # <- also not a decimal, but Decimal/int is defined

这就是您不使用eval：）

的原因

没有eval：

import math
import decimal as deci

# defines variables

eul = 0
step = 0

# queries for input

sigdig = int(raw_input("Evaluate number e to n significant digits (up to 27): "))
sigdig2 = deci.Decimal(1) / deci.Decimal(10 ** sigdig)

deci.getcontext().prec = (sigdig + 1)

# evaluates e

while deci.Decimal(1) / deci.Decimal(math.factorial(step)) > sigdig2:
    eul += deci.Decimal(1) / deci.Decimal(math.factorial(step))
    step +=1

#prints the result

print
print 'e = %s' % eul

$ python e.py
Evaluate number e to n significant digits (up to 27): 40

e = 2.7182818284590450907955982984276488423347

Evaluate number e to n significant digits (up to 27): 1000

e = 2.71828182845904523536028747135266249775724709369995957496696762772407663035
35475945713821785251664274274663919320030599218174135966290435729003342952605956
30738132328627943490763233829880753195251019011573834187930702154089149934884167
50924476146066808226480016847741185374234544243710753907774499206955170276183860
62613313845830007520449338265602976067371132007093287091274437470472306969772093
10141692836819025515108657463772111252389784425056953696770785449969967946864454
90598793163688923009879312773617821542499922957635148220826989519366803318252886
93984964651058209392398294887933203625094431173012381970684161403970198376793206
83282376464804295311802328782509819455815301756717361332069811250996181881593041
69035159888851934580727386673858942287922849989208680582574927961048419844436346
32449684875602336248270419786232090021609902353043699418491463140934317381436405
46253152096183690888707016768396424378140592714563549061303107208510383750510115
7477041718986106873969655212671546889570350362

使用十进制模块不能超过27位小数

1 个答案: