Difference Between Python Float and Numpy Float32
What Is the Difference Between the Built in Float and Numpy. Float32? Example a = 58682.7578125 Print Type(A) Print a Print Type(Numpy. Float32(A)) Print...
What is the difference between the built in float and numpy.float32?
Example
a = 58682.7578125
print type(a)
print a
print type(numpy.float32(a))
print numpy.float32(a)
Output:
<type 'float'>
58682.7578125
<type 'numpy.float32'>
58682.8
I've found here that numpy.float32 is:
float32 Single precision float: sign bit, 8 bits exponent, 23 bits mantissa
didn't find what the built in float format is.
2 Answers
Python's standard float type is a C double:
NumPy's standard numpy.float is the same, and is also the same as numpy.float64.
Data type-wise numpy floats and built-in Python floats are the same, however boolean operations on numpy floats return np.bool_ objects, which always return False for val is True. Example below:
In [1]: import numpy as np
...: an_np_float = np.float32(0.3)
...: a_normal_float = 0.3
...: print(a_normal_float, an_np_float)
...: print(type(a_normal_float), type(an_np_float))
0.3 0.3
<class 'float'> <class 'numpy.float32'>
Numpy floats can arise from scalar output of array operations. If you weren't checking the data type, it is easy to confuse numpy floats for native floats.
In [2]: criterion_fn = lambda x: x <= 0.5
...: criterion_fn(a_normal_float), criterion_fn(an_np_float)
Out[2]: (True, True)
Even boolean operations look correct. However the result of the numpy float isn't a native boolean datatype, and thus can't be truthy.
In [3]: criterion_fn(a_normal_float) is True, criterion_fn(an_np_float) is True
Out[3]: (True, False)
In [4]: type(criterion_fn(a_normal_float)), type(criterion_fn(an_np_float))
Out[4]: (bool, numpy.bool_)
According to this github thread, criterion_fn(an_np_float) == True will evaluate properly, but that goes against the PEP8 style guide.
Instead, extract the native float from the result of numpy operations. You can do an_np_float.item() to do it explicitly (ref: this SO post) or simply pass values through float().
Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.
