数字格式从美分到美元

Question

我正在尝试使用Python 2.7的字符串格式输出美元十个苹果的成本，其中单位价格以美分提供。

我希望total_apple_cost的值为"10.00"，但它是"1.001.001.001.001.001.001.001.001.001.00"。

我已经包含了其他变量的测试表明，他们都走出预期：

# define apple cost in cents 
apple_cost_in_cents = 100 
# define format string 
cents_to_dollars_format_string = '{:,.2f}' 
# convert 100 to 1.00 
apple_cost_in_dollars = cents_to_dollars_format_string.format(apple_cost_in_cents/100.) 
# assign value of 'apple_cost_in_dollars' to 'apple_cost' 
apple_cost = apple_cost_in_dollars 
# calculate the total apple cost 
total_apple_cost = 10 * apple_cost 

# print out the total cost 
print 'total apple cost: ' + str(total_apple_cost) + '\n' 

#testing 
print 'cost in cents: ' + str(apple_cost_in_cents) + '\n' 
print 'cost in dollars: ' + str(apple_cost_in_dollars) + '\n' 
print 'apple cost: ' + str(apple_cost) + '\n' 

解决方案：

谢谢你的回答下面这既表明变量“ apple_cost_in_dollars'是一个字符串。

我的解决办法是让它浮动，保持代码的其余部分几乎相同：

apple_cost_in_cents = 100 
cents_to_dollars_format_string = '{:,.2f}' 
apple_cost_in_dollars = float(cents_to_dollars_format_string.format(apple_cost_in_cents/100.)) 
apple_cost = apple_cost_in_dollars 
total_apple_cost = 10 * apple_cost 

print 'cost in cents: ' + str(apple_cost_in_cents) + '\n' 

print 'cost in dollars: $''{:,.2f}'.format(apple_cost_in_dollars) + '\n' 

print 'apple cost: $''{:,.2f}'.format(apple_cost) + '\n' 

print 'total apple cost: $''{:,.2f}'.format(total_apple_cost) + '\n' 

Answer 1

这是因为apple_cost_in_dollars是一个字符串，请参见下面

In [9]: cost = '1' 

In [10]: cost * 10 
Out[10]: '1111111111' 

In [11]: cost = int('1') 

In [12]: cost * 10 
Out[12]: 10 

Answer 2

apple_cost是一个字符串，你乘以10（它简单地重复字符串10次）。在将其格式化为字符串之前，先将其转换为美元。

>>> apple_cost_in_cents = 100 
>>> cents_to_dollars_format_string = '{:,.2f}' 
>>> total_apple_cost_in_dollars_as_string = cents_to_dollars_format_string.format(10*apple_cost_in_cents/100.0) 
>>> total_apple_cost_in_dollars_as_string 
'10.00' 

如果你想带格式的货币，你可以看看的locale模块并专门locale.currency功能走得更远。

Answer 3

>>> import locale 
>>> apple_cost_in_cents = 100 
>>> locale.setlocale(locale.LC_ALL, '') 
'en_US.UTF-8' 
>>> locale.currency(apple_cost_in_cents * 10/100) 
'$10.00' 

Answer 4

它被格式化为一个字符串（文本）。所以，如果你写10 * string_variable，它只是重复该字符串10次。最简单的方法就是改变这一行：

total_apple_cost = 10 * apple_cost

到：

total_apple_cost = cents_to_dollars_format_string.format(10 * apple_cost_in_cents/100)