Use Python Numeric Variables in MATLAB
This example shows how to use Python® numeric types in MATLAB®.
Use Python Numeric Types in MATLAB
When calling a Python function that takes a 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 Python math
module, pass a MATLAB double value.
pynum = py.math.radians(90)
pynum = 1.5708
For functions that return Python float
types, MATLAB automatically converts this type to double.
class(pynum)
ans = 'double'
For Python functions returning integer types, MATLAB automatically converts this type to int64
. For example, the bit_length
function returns the number of bits necessary to represent an integer in binary as an int
value.
py.int(intmax).bit_length
ans = int64
31
Call Python Methods with Numeric iterable
Arguments
The Python math.fsum
function sums floating-point values in an iterable
input argument. You can pass a MATLAB vector to this function. For example, open the MATLAB patients.mat
data file and read the numeric array Height
.
load patients.mat
class(Height)
ans = 'double'
size(Height)
ans = 1×2
100 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 Python array
Types in MATLAB
Suppose that you have a Python function that returns the following Python array.array
of 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 pass P
to the MATLAB function sum
, convert P
to a MATLAB array of type double.
sum(double(P))
ans = 15
Use Python Integer array
Types in MATLAB
Suppose that you have this Python array. Call the Python reverse
function 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 a double
type. 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 Python datetime
function, Python reads them as float
types 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