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Understand Python Function Arguments

Your Python® documentation shows you how to call a Python function. Python function signatures look similar to MATLAB® function signatures. However, Python has syntax which might be unfamiliar to MATLAB users.

Positional Arguments

A positional argument is passed by position. These arguments appear at the beginning of a function signature.

Python SignatureMATLAB Usage

Argument X is required.

>> py.abs(-99)

Some functions accept an arbitrary sequence of positional arguments, including no arguments. In Python, these arguments are defined by prepending the name with the * character.

Python SignatureMATLAB Usage

The iterables argument is not required, in which case, the function returns a zero length iterator.

Aggregate elements from two lists.
>> py.itertools.izip(... py.list({1:10}),py.list({'a','b'}));

Create zero length iterator.
>> py.itertools.izip;


>> words = {'Hello','World!'};
>> py.print(words{:})

Keyword Arguments

A keyword argument is preceded by an identifier. Keyword arguments, also called named arguments, can be specified in any order. Keyword arguments are like name-value pairs in MATLAB. Use the MATLAB pyargs function to create keyword arguments for Python functions.

Python SignatureMATLAB Usage


sep, end, and file are keyword arguments.

Change the value of end.
>> py.print('string',pyargs('end','--'))

This example uses the default value for the file keyword. Create some text variables.

x1 = py.str('c:');
x2 = py.os.curdir;
x3 = py.os.getenv('foo');
c: . None

To display the values on separate lines, use newline, \n, as a separator.


To change sep to an empty string and change the end value to display THE END, type:

py.print(x1,x2,x3,pyargs('end', sprintf(' THE END\n'),'sep',py.str))
c:.None THE END

Arbitrary Number of Keyword Arguments

Python defines an arbitrary number of keyword arguments by prepending the name with ** characters.

Python SignatureMATLAB Usage


>> D = py.dict(pyargs('Joe',100,'Jack',101))

Optional Arguments

An optional argument is a non-required argument.

Python SignatureMATLAB Usage

Argument step is optional.

>> py.random.randrange(1,100)

Optional arguments can have default values. A default value is indicated by an equal sign = with the default value.

Python SignatureMATLAB Usage


The default value for file is sys.stdout.

Print two values using default keyword values.
>> py.print(2,'2')

See Also