[Solved] What kind of number 9.00000000e-01 is?

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>>> import numpy as np
>>> x = np.arange(-1,1,0.1)
>>> print(x)
[ -1.00000000e+00  -9.00000000e-01  -8.00000000e-01  -7.00000000e-01
-6.00000000e-01  -5.00000000e-01  -4.00000000e-01  -3.00000000e-01
-2.00000000e-01  -1.00000000e-01  -2.22044605e-16   1.00000000e-01
 2.00000000e-01   3.00000000e-01   4.00000000e-01   5.00000000e-01
 6.00000000e-01   7.00000000e-01   8.00000000e-01   9.00000000e-01]
>>> type(x[0])
<type 'numpy.float64'>

>>> print(x.tolist())
[-1.0, -0.9, -0.8, -0.7000000000000001, -0.6000000000000001, -0.5000000000000001,         -0.40000000000000013, -0.30000000000000016, -0.20000000000000018, -0.1000000000000002, -2.220446049250313e-16, 0.09999999999999964, 0.19999999999999973, 0.2999999999999998, 0.3999999999999997, 0.49999999999999956, 0.5999999999999996, 0.6999999999999997, 0.7999999999999996, 0.8999999999999995]
>>> type(x.tolist()[0])
<type 'float'>

The type is initially a numpy float64.

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solved What kind of number 9.00000000e-01 is?