Use Python Numeric Types in MATLAB

当调用一个Python函数numeric input argument, MATLAB converts double values into types that best represent the data to the Python language. For example, to call trigonometry functions in the Pythonmathmodule, pass a MATLAB double value.

pynum = py.math.radians(90)

pynum = 1.5708

For functions that return Pythonfloattypes, MATLAB automatically converts this type to double.

class(pynum)

ans = 'double'

For Python functions returning integer types, MATLAB automatically converts this type toint64. For example, thebit_lengthfunction returns the number of bits necessary to represent an integer in binary as anintvalue.

py.int(intmax).bit_length

ans =int6431

Call Python Methods with NumericiterableArguments

The Pythonmath.fsumfunction sums floating-point values in aniterableinput argument. You can pass a MATLAB vector to this function. For example, open the MATLABpatients.matdata file and read the numeric arrayHeight.

loadpatients.matclass(Height)

ans = 'double'

size(Height)

ans =1×2100 1

When you pass this argument to Python, MATLAB automatically converts the numeric values to Python numeric values and Python iterates over the vector values.

py.math.fsum(Height)

ans = 6707

Use PythonarrayTypes in MATLAB

Suppose that you have a Python function that returns the following Pythonarray.arrayof type double.

P = py.array.array('d', 1:5)

P = Python array with properties: itemsize: 8 typecode: [1×1 py.str] array('d', [1.0, 2.0, 3.0, 4.0, 5.0])

To passPto the MATLAB functionsum, convertPto a MATLAB array of type double.

sum(double(P))

ans = 15

Use Python IntegerarrayTypes in MATLAB

Suppose that you have this Python array. Call the Pythonreversefunction on the array, then convert the result to a MATLAB array.

arr = py.array.array('i',[int32(5),int32(1),int32(-5)])

arr = Python array with properties: itemsize: 4 typecode: [1×1 py.str] array('i', [5, 1, -5])

arr.reverse A = int32(arr)

A =1×3 int32 row vector-5 1 5

Default Numeric Types

By default, a number in MATLAB is adoubletype. By default, a number (without a fractional part) in Python is an integer type. This difference can cause confusion when passing numbers to Python functions.

For example, when you pass these MATLAB numbers to the Pythondatetimefunction, Python reads them asfloattypes and displays an error:

d = py.datetime.date(2014,12,31)

Python Error: TypeError: integer argument expected, got float

To correct the error, explicitly convert each number to an integer type:

d = py.datetime.date (int32 (2014), int32 (12), int32 (31))

d = Python date with properties: day: 31 month: 12 year: 2014 2014-12-31

Why Do I See Properties When I Display a Number?

MATLAB displays all Python types as objects, which includes a list of object properties. For numeric types, MATLAB displays the expected output value on the last line.

py.int(5)

ans = Python int with properties: denominator: 1 imag: 0 numerator: 5 real: 5 5