118 lines
2.8 KiB
Markdown
118 lines
2.8 KiB
Markdown
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---
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title: Python Floating Point Numbers
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localeTitle: Python浮点数
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---
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有关浮点数的一般信息以及它们如何在Python中工作，可以在[这里](https://docs.python.org/3/tutorial/floatingpoint.html)找到。
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几乎所有Python的实现都遵循IEEE 754规范：二进制浮点运算标准。更多信息可在[IEEE网站](http://grouper.ieee.org/groups/754/)上找到。
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可以使用[浮点文字](https://docs.python.org/3/reference/lexical_analysis.html#floating-point-literals)创建浮动对象：
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```
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>>> 3.14
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3.14
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>>> 314\. # Trailing zero(s) not required.
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314.0
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>>> .314 # Leading zero(s) not required.
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0.314
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>>> 3e0
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3.0
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>>> 3E0 # 'e' or 'E' can be used.
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3.0
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>>> 3e1 # Positive value after e moves the decimal to the right.
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30.0
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>>> 3e-1 # Negative value after e moves the decimal to the left.
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0.3
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>>> 3.14e+2 # '+' not required but can be used for exponent part.
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314.0
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```
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数字文字不包含符号，但是可以通过在文字前面没有空格的一元`-` （减号）运算符作为前缀来创建负浮点对象。
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```
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>>> -3.141592653589793
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-3.141592653589793
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>>> type(-3.141592653589793)
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<class 'float'>
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```
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同样，正浮点对象可以使用一元`+ (`加号）运算符作为前缀，在文字前没有空格。通常`+`省略：
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```
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>>> +3.141592653589793
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3.141592653589793
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```
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请注意，前导零和尾随零对浮点文字有效
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```
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>>> 0.0
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0.0
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>>> 00.00
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0.0
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>>> 00100.00100
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100.001
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>>> 001e0010 # Same as 1e10
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10000000000.0
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```
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[`float`构造函数](https://docs.python.org/3/library/functions.html#float)是另一种创建`float`对象的方法。
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在可能的情况下，首选创建具有浮点文字的`float`对象：
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```
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>>> a = 3.14 # Prefer floating point literal when possible.
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>>> type(a)
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<class 'float'>
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>>> b = int(3.14) # Works but unnecessary.
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>>> type(b)
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<class 'float'>
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```
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但是，float构造函数允许从其他数字类型创建float对象：
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```
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>>> a = 4
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>>> type(a)
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<class 'int'>
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>>> print(a)
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4
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>>> b = float(4)
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>>> type(b)
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<class 'float'>
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>>> print(b)
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4.0
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>>> float(400000000000000000000000000000000)
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4e+32
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>>> float(.00000000000000000000000000000004)
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4e-32
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>>> float(True)
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1.0
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>>> float(False)
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0.0
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```
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`float`构造函数还将从表示数字文字的字符串中创建`float`对象：
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```
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>>> float('1')
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1.0
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>>> float('.1')
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0.1
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>>> float('3.')
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3.0
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>>> float('1e-3')
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0.001
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>>> float('3.14')
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3.14
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>>> float('-.15e-2')
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-0.0015
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```
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`float`构造函数也可用于表示`NaN` （非数字），负`infinity`和`infinity`数字表示（注意这些字符串不区分大小写）：
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```
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>>> float('nan')
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nan
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>>> float('inf')
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inf
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>>> float('-inf')
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-inf
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>>> float('infinity')
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inf
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>>> float('-infinity')
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-inf
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```
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