Yarpiz Structure (ypstruct)

A simple and easy-to-use MATLAB-like structure type for Python

Installation

You can use pip to install ypstruct:

pip install ypstruct

If you want to install from source code, you can download from github or simply use:

git clone https://github.com/smkalami/ypstruct

and then, run this:

python setup.py install

Sample Usage

The structure is defined by struct class. Also an alias of this class is defined and available as structure.

A simple usage code of ypstruct.struct follows.

from ypstruct import *

p = struct()
p.x = 3
p.y = 4
p.A = p.x * p.y
print(p)

The output will be:

struct({'x': 3, 'y': 4, 'A': 12})

Here, after importing the struct (and its alias structure) from ypstruct, an instance of struct is created and then fields x and y are defined. Then, a new field A is added to the structure. Finally, the string representation of the struct is printed.

In the previous code, you can simply use the following method to create and initialize the structure.

p = struct(x=3, y=4)
p.A = p.x * p.y

dict vs. struct

Actually struct is a subclass of built-in dictionary type dict, and it can be converted to or created from dict objects.

You can convert dict objects to struct as follows:

my_dict = {'x':3, 'y':4}
p = struct(my_dict)

Also, struct object can be converted to dict as well:

p = struct(x=3, y=4)
p.z = 12
my_dict = dict(p)
print(my_dict)

The output will be this:

{'x': 3, 'y': 4, 'z': 12}

Merging Structures

It is possible to merge two struct objects. For example let's define two structures as:

a = struct(x=1, y=2, z=3)
b = struct(y=5, t=20, u=30)

We can merge these structure using + operator:

c = a + b
print(c)

The output will be:

struct({'x': 1, 'y': 5, 'z': 3, 't': 20, 'u': 30})

List of the Methods

In this part, we are going to discuss the methods implemented and available in struct class and its alias structure. You can use these methods with any instance of struct class. Additionally, because the struct class is a subclass of dict, all of the methods defined in the dict class are available too.

fields() Method

The fields() method returns a list of fields defined in structure. An example usage follows:

p = struct(x=3, y=4)
print(p.fields())

The output will be:

['x', 'y']

add_field() Method

A new field can be added using add_field() method. This method accepts two input arguments: field name and its value. The value is optional and if it is ignored, then value is assumed to be None. A sample code follows:

p = struct(x=3, y=4)
p.add_field('z', 12)
p.add_field('L')
print(p)

The output of this code will be:

struct({'x': 3, 'y': 4, 'z': 12, 'L': None})

Instead of using the add_field() method, it is possible to use . and = operators. For example, the above-mentioned code can be simplified as this:

p = struct(x=3, y=4)
p.z = 12
p.L = None
print(p)

The result will be the same.

remove_field() Method

A field can be removed from a struct object using remove_field() method. This method gets a field name and it removes (deletes) the specified field. An example is given below:

p = struct(x=3, y=4, z=12)
print('Before remove_field: {}'.format(p))
p.remove_field('z')
print('After remove_field: {}'.format(p))

The output will be this:

Before remove_field: struct({'x': 3, 'y': 4, 'z': 12})
After remove_field: struct({'x': 3, 'y': 4})

repeat() Method: Repeating a Structure

Sometimes we need to repeat/replicate a structure. For example, assume that we are going to implement an Evolutionary Algorithm and we defined the individuals as struct objects. First we need to create a template:

empty_individual = struct(pos=None, fval=None)

Then we can initialize the population array using following code:

pop_size = 10
pop = empty_individual.repeat(pop_size)

This code uses the repeat() method to initialize a list of distinct struct objects with the same data fields. Instead of using repeat() method, simply we can use * operator to perform replication:

pop = empty_individual * pop_size

copy() and deepcopy() Methods

The struct is a reference type. To have a copy of a struct object, you cannot simply use assignment operator. To create copies of structure objects, two methods are implemented in struct class: copy() and deepcopy(). The first one gives us a shallow copy of the struct object. But using deepcopy(), as the name of the method says, we can create deep copies of structure objects.