# Hello, World!

This chapter discusses your first steps in the world of `molli`-enabled computing.

````{note}
All examples of code showin in these sections assumes that molli is imported the following way:

```python
import molli as ml
```
````

## Overview

`molli` package provides a user-friendly and easily extensible object-oriented code that features objects that have familiar to chemists meaning and behavior. These classes are summarized below ({ref}`chem_inherit`) for the convenience of user. For detailed documentation, check out the next chapter.

```{figure} ../imgs/chem_inheritance.png
:name: chem_inherit
:alt: molli_inherit
:class: bg-primary
:width: 300px
:align: center

Module `molli.chem` class inheritance diagram

```

## Input and output
### Reading / writing molecule objects from files

molli *natively* supports only `.mol2` and `.xyz` files for molecule reading. Through the powerful OpenBabel library interface, arbitrary file formats can be read. The following example shows one possible way loading a `.mol2` file:

```python
mol = ml.Molecule.load_mol2("./path/to/file.mol2")
```

Using a syntax that would be familiar to users of `json` and other libraries, one can also serialize molecules:

```python
with open("./path/to/other.mol2", "wt") as f:
    mol.dump_mol2("f")
```

```{important}
Molli implements objects that are more complex than what some of the existing chemical formats, including mol2, can encode.
It is therefore recommended to exercise caution.
The best way to save molli objects is in the libraries (see below.)
```

### Default files

molli provides some files for testing and prototyping purposes in the `molli.files` package.
They are installed with the package, and one can access their full path without knowing the exact installation directory:

```python
>>> ml.files.dendrobine_mol2
PosixPath('/home/username/dev/molli/molli/files/dendrobine.mol2')
```

One can therefore access the test molecule files conveniently:
```python
mol = ml.Molecule.load_mol2(ml.files.dendrobine_mol2)
```