graphviz-managed 1.0.0
Manipulate Graphviz graphs in Python prior to rendering
License: Apache-2.0
Keywords: graphs,graphviz

# Manipulate Graphviz graphs in Python prior to rendering

Graphviz wrapper that allows to manage graph objects in Python prior to
translating them into dot language.

## Rationale

Unfortunately, both [graphviz] and [diagrams] packages do not allow any
operations on graphs besides adding nodes and edges. If you want to loop
through all graph nodes or edges to calculate some extra attributes - you're
out of luck.

This small library builds graphs as Python objects prior to translating them
into dot language. That means you can manipulate your graphs programmatically
in any way you want.

[graphviz]: https://graphviz.readthedocs.io/en/stable/manual.html
[diagrams]: https://diagrams.mingrammer.com/


## Usage

### Basic usage

This is nothing special, [diagrams] offers a lot more possibilities here.

```python
from graphviz_managed import Graph
graph = Graph(label='<<b>Sample Graph #1</b>>')
node = graph.node
foo = node(label='Foo!')
bar = node(label='BAR', fontcolor='red', penwidth=1.5)
foo >> bar >> foo
graph.render('basic.svg')
```

[![sample graph output](samples/basic.svg)](samples/basic.py)


### Change node style based on number of incoming/outgoing edges

Dynamic graph manipulation is impossible with [graphviz] or [diagrams],
but is rather straightforward with this library:

```python
from graphviz_managed import Graph
graph = Graph(label='Highlight graph entry points', rankdir='LR')
node = graph.node

# Define a larger graph
a = node(label='a')
b = node(label='b')
c = node(label='c')
d = node(label='d')
e = node(label='e')
f = node(label='f')
a >> [b, e]
c >> [b, e]
d >> a
e >> f
f >> [b, a]

# Highlight nodes with no incoming edges
from collections import defaultdict
incoming_count = defaultdict(int)
for edge in graph.edges:
    incoming_count[edge.end] += 1
for node in graph.nodes:
    if incoming_count[node] == 0:
        node.attrs.color = 'darkgreen'
        node.attrs.fontcolor = 'darkgreen'
        node.attrs.style = 'filled'
        node.attrs.fillcolor = 'beige'

# Save output
graph.render('count.svg')
```

[![sample graph output](samples/count.svg)](samples/count.py)

### Break long labels into multiple lines

Providing custom factories for nodes and edges allows for some interesting
customizations.

```python
from graphviz_managed import Graph
from graphviz_managed.custom import WrapLongLabelNode
graph = Graph(node_cls=WrapLongLabelNode, rankdir='LR', node_attrs=dict(shape='box'))
a = graph.node(label='Short text')
b = graph.node(label='Long label that will be wrapped into multiple lines')
c = graph.node(label='CantWrapSpecialCamelCaseWordsWithoutSpaces')
d = graph.node(label='CantWrapSpecialCamelCaseWordsWithoutSpaces but can wrap elsewhere')
a >> b >> c >> d
graph.render('labels.svg')
```

[![sample graph output](samples/labels.svg)](samples/labels.py)

### Wrapper for [diagrams] package

graphviz-managed can be extended to support other graph rendering libraries.
[Here is](src/graphviz_managed/diagrams.py) how it's done for [diagrams].
Resulting objects may be manipulated in the same way, enjoying all pre-rendering
freedoms demonstrated above.

```python
from graphviz_managed.diagrams import Diagram
diag = Diagram(label='Fancy node templates from https://pypi.org/project/diagrams/', pad=0.1)
node = diag.node
lb = node(kind='aws.network.ELB', label='lb')
web = node(kind='aws.compute.EC2', label='web')
db = node(kind='aws.database.RDS', label='db')
store = node(kind='aws.storage.S3', label='store')
lb >> web >> db >> store
diag.render('diag.png')
```

[![sample graph output](samples/diag.png)](samples/diag.py)

More samples can be found in [tests/](tests/) directory.


## Support and contributing

If you need help with using this library or including it into your project,
please create **[an issue][issues]**.
Issues are also the primary venue for reporting bugs and posting feature
requests. General discussion related to this project is also acceptable and
very welcome!

In case you wish to contribute code or documentation, feel free to open
**[a pull request](https://github.com/sio/graphviz-managed/pulls)**. That would
certainly make my day!

I'm open to dialog and I promise to behave responsibly and treat all
contributors with respect. Please try to do the same, and treat others the way
you want to be treated.

If for some reason you'd rather not use the issue tracker, contacting me via
email is OK too. Please use a descriptive subject line to enhance visibility
of your message. Also please keep in mind that public discussion channels are
preferable because that way many other people may benefit from reading past
conversations. My email is visible under the GitHub profile and in the commit
log.

[issues]: https://github.com/sio/graphviz-managed/issues


## License and copyright

Copyright 2021 Vitaly Potyarkin

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.