我的小数对于%E来说太大了，所以我不得不即兴发挥:

def format_decimal(x, prec=2):
    tup = x.as_tuple()
    digits = list(tup.digits[:prec + 1])
    sign = '-' if tup.sign else ''
    dec = ''.join(str(i) for i in digits[1:])
    exp = x.adjusted()
    return '{sign}{int}.{dec}e{exp}'.format(sign=sign, int=digits[0], dec=dec, exp=exp)

下面是一个用法示例:

>>> n = decimal.Decimal(4.3) ** 12314
>>> print format_decimal(n)
3.39e7800
>>> print '%e' % n
inf

def formatE_decimal(x, prec=2):
    """ Examples:
    >>> formatE_decimal('0.1613965',10)
    '1.6139650000E-01'
    >>> formatE_decimal('0.1613965',5)
    '1.61397E-01'
    >>> formatE_decimal('0.9995',2)
    '1.00E+00'
    """
    xx=decimal.Decimal(x) if type(x)==type("") else x 
    tup = xx.as_tuple()
    xx=xx.quantize( decimal.Decimal("1E{0}".format(len(tup[1])+tup[2]-prec-1)), decimal.ROUND_HALF_UP )
    tup = xx.as_tuple()
    exp = xx.adjusted()
    sign = '-' if tup.sign else ''
    dec = ''.join(str(i) for i in tup[1][1:prec+1])   
    if prec>0:
        return '{sign}{int}.{dec}E{exp:+03d}'.format(sign=sign, int=tup[1][0], dec=dec, exp=exp)
    elif prec==0:
        return '{sign}{int}E{exp:+03d}'.format(sign=sign, int=tup[1][0], exp=exp)
    else:
        return None

这是一个“简单”答案和评论的综合列表。

PYTHON 3

from decimal import Decimal

x = '40800000000.00000000000000'
# Converted to Float
x = Decimal(x)

# ===================================== # `Dot Format`
print("{0:.2E}".format(x))
# ===================================== # `%` Format
print("%.2E" % x)
# ===================================== # `f` Format
print(f"{x:.2E}")
# =====================================
# ALL Return: 4.08E+10
print((f"{x:.2E}") == ("%.2E" % x) == ("{0:.2E}".format(x)))
# True
print(type(f"{x:.2E}") == type("%.2E" % x) == type("{0:.2E}".format(x)))
# True
# =====================================

或无进口

# NO IMPORT NEEDED FOR BASIC FLOATS
y = '40800000000.00000000000000'
y = float(y)

# ===================================== # `Dot Format`
print("{0:.2E}".format(y))
# ===================================== # `%` Format
print("%.2E" % y)
# ===================================== # `f` Format
print(f"{y:.2E}")
# =====================================
# ALL Return: 4.08E+10
print((f"{y:.2E}") == ("%.2E" % y) == ("{0:.2E}".format(y)))
# True
print(type(f"{y:.2E}") == type("%.2E" % y) == type("{0:.2E}".format(y)))
# True
# =====================================

比较

# =====================================
x
# Decimal('40800000000.00000000000000')
y
# 40800000000.0

type(x)
# <class 'decimal.Decimal'>
type(y)
# <class 'float'>

x == y
# True
type(x) == type(y)
# False

x
# Decimal('40800000000.00000000000000')
y
# 40800000000.0

所以对于Python 3，你现在可以在这三种方式中任意切换。

我喜欢:

print("{0:.2E}".format(y))

我的小数对于%E来说太大了，所以我不得不即兴发挥:

def format_decimal(x, prec=2):
    tup = x.as_tuple()
    digits = list(tup.digits[:prec + 1])
    sign = '-' if tup.sign else ''
    dec = ''.join(str(i) for i in digits[1:])
    exp = x.adjusted()
    return '{sign}{int}.{dec}e{exp}'.format(sign=sign, int=digits[0], dec=dec, exp=exp)

下面是一个用法示例:

>>> n = decimal.Decimal(4.3) ** 12314
>>> print format_decimal(n)
3.39e7800
>>> print '%e' % n
inf

这对我来说效果最好:

import decimal
'%.2E' % decimal.Decimal('40800000000.00000000000000')
# 4.08E+10

下面是一个使用format()函数的例子:

>>> "{:.2E}".format(Decimal('40800000000.00000000000000'))
'4.08E+10'

除了format，你还可以使用f-strings:

>>> f"{Decimal('40800000000.00000000000000'):.2E}"
'4.08E+10'

官方文档 原始格式()提案