# Modules in Python

## Creating Modules

As our program grows we should split our code across multiple files. We refer to each file as a module. A module should contain related data, functions, and objects. 

```python
def calc_tax():
	pass

def calc_shipping():
	pass
```
<hr>

## Importing a module

Now we can import those functions to this file.

```python
# import
from sales import calc_tax

# use it
calc_tax()

# ==============================

# import multiple functions 
from sales import calc_tax, calc_shipping

# ==============================

# import everything 
from sales import *
```

**another way of importing**

```python
# import
import sales 

# use
sales.calc_tax()
```

> Even if we imported only one function then also the entire module needs to be loaded.

---

## Compiled Python Files

When we will compile the ```app.py``` file using the command ```python app.py ``` then python will create a folder names ```__pycache__ ```

In this folder, there will be a compiled version of the module that you just imported in the app.py file.

This is done to speed up compilation. And this will speed up the loading of the module. 

> This will not speed up the performance of the program.

```app.py``` is not cached because the entry file is always recompiled. 

---

## Module Search Path

If the python compiler does not find the module in the current folder then it will search for the file in a bunch of predefined folders. 

The built in modules like sys are kept in these folders. 

---

## Package

Packages are used if the file that we want to use is inside a sub folder. 

The folder structure looks like this. 


![Untitled.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1617440839931/m7F3eVWFLc.png)

> We can not do this -

```python
# we can not do this 
from ./ecommerce/sales import tax
```

We have to create a  ```__init__.py``` file in the ecommerce folder. When we create this file then python will think of this folder as a package. 

> A package is a folder that contains one or more modules.

So a module is a file and a package is a folder. 

The ```__init__.py``` file is empty.

![Untitled 1.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1617440906061/eUbMRUTOz.png)

Now you can import and use it in three ways

```python
# way 1
import ecommerce.sales

ecommerce.sales.tax()

# =========================
# way 2 
from ecommerce.sales import tax, sales

tax()

# =========================
# way 3
import sales from ecommerce

sales.tax()
```

## Sub-packages

Now we have to create another ```__init__.py``` file in the sub folder also

Our folder structure is like this 


![Untitled 2.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1617440921698/w8_v19iV2.png)
now import like this

```python
from ecommerce.shopping import sales
```

---

## Intra Package Reference

This simply means, using one package into another package. 


![Untitled 3.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1617440933361/IOjIHk73C.png)

In our sales modules, we want to use the contact module.

**we can use absolute import**

```python
from ecommerce.customer import contact
contact.customer()
```

**we can use relative import**

```python
from ../customer import contact
contact.customer()
```

---

## The dir Function

This function will give us all the functions that are defined in a module 

```python
from ecommerce.shopping import sales 

print(dir(sales))
```

some functions such as```__name__``` , ```__package__``` , etc are already defined for us. 

```python
print(__name__)
print(__package__)
print(__file__)

'''
These functions give us the file name of the module,
the package name and the address of the module 
'''
```

> The name of the module that starts our program is always ```__main__```