問題描述
基本上，我將浮點數轉換為整數，但我并不總是有預期值.
Basically, I'm converting a float to an int, but I don't always have the expected value.
這是我正在執行的代碼:
Here's the code I'm executing:
x = 2.51
print("--------- 251.0")
y = 251.0
print(y)
print(int(y))
print("--------- 2.51 * 100")
y = x * 100
print(y)
print(int(y))
print("--------- 2.51 * 1000 / 10")
y = x * 1000 / 10
print(y)
print(int(y))
print("--------- 2.51 * 100 * 10 / 10")
y = x * 100 * 10 / 10
print(y)
print(int(y))
x = 4.02
print("--------- 402.0")
y = 402.0
print(y)
print(int(y))
print("--------- 4.02 * 100")
y = x * 100
print(y)
print(int(y))
print("--------- 4.02 * 1000 / 10")
y = x * 1000 / 10
print(y)
print(int(y))
print("--------- 4.02 * 100 * 10 / 10")
y = x * 100 * 10 / 10
print(y)
print(int(y))
這是結果(第一個值是操作的結果，第二個值是相同操作的 int()):
And here's the result (first value is the result of the operation, second value is int() of the same operation):
--------- 251.0
251.0
251
--------- 2.51 * 100
251.0
250
--------- 2.51 * 1000 / 10
251.0
251
--------- 2.51 * 100 * 10 / 10
251.0
250
--------- 402.0
402.0
402
--------- 4.02 * 100
402.0
401
--------- 4.02 * 1000 / 10
402.0
401
--------- 4.02 * 100 * 10 / 10
402.0
401
2.51 和 4.02 是導致 2.50 -> 5.00 范圍內奇怪行為的唯一值.當給定相同的操作時，該范圍內的每隔兩個數字值轉換為 int 沒有任何問題.
2.51 and 4.02 are the only values that lead to that strange behaviour on the 2.50 -> 5.00 range. Every other two digits value in that range converts to int without any problem when given the same operations.
那么，我錯過了什么導致這些結果?順便說一下，我使用的是 Python 2.7.2.
So, what am I missing that leads to those results? I'm using Python 2.7.2 by the way.
推薦答案
2.51 * 100 = 250.999999999997
int() 函數只是截斷小數點處的數字，得到 250.使用
The int() function simply truncates the number at the decimal point, giving 250. Use
int(round(2.51*100))
獲取 251 作為整數.一般來說，浮點數不能精確表示.因此，應注意舍入誤差.如前所述，這不是 Python 特有的問題.這是所有計算機語言中反復出現的問題.
to get 251 as an integer. In general, floating point numbers cannot be represented exactly. One should therefore be careful of round-off errors. As mentioned, this is not a Python-specific problem. It's a recurring problem in all computer languages.
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