[CentralOH] May Monthly meeting this Monday -- From the Pyramids to Python: Architecture to cope with large projects

[Neil Ludban]

Here are all the software links from the presentation, plus the text
of a few key slides, and the code for the lxml utility functions.


To clarify my response to one of the questions asked, the multi-tier
architecture and layer responsibities given in the slides is a good
starting point for any application since it separates interacting with
the outside world, making decisions, and handling data.  The "force
fit" remark was intended as a recommendation to initially break the
functionality into layers, later reorganizing each layer with more
elegant pyramids/facades patterns.  With practice in any domain, the
working patterns become more familiar and it's easier to plan the big
parts of the architecture on paper before starting to write code.


https://sedimental.org/
    10_myths_of_enterprise_python.html
        - paypal, ca 2014-12
    esp.html
        - "Enterprise Software with Python"
          O'Reilly lectures

https://www.packtpub.com/
    application-development/software-architecture-python

https://www.youtube.com/watch?v=DJtef410XaM
    - PyOhio 2014
    - Brandon Rhodes
    - "The Clean Architecture in Python"

https://en.wikipedia.org/
    wiki/Robert_C._Martin
https://8thlight.com/blog/uncle-bob/
    2012/08/13/the-clean-architecture.html
    2011/09/30/Screaming-Architecture.html

https://en.wikipedia.org/
    wiki/The_Mythical_Man-Month

http://www.cs.yale.edu/
    homes/perlis-alan/quotes.html
    "Epigrams in Programming"
    ACM SIGPLAN, September 1982

https://en.wikipedia.org/

    wiki/Cohesion_(computer_science)
    wiki/Coupling_(computer_programming)

    wiki/Separation_of_mechanism_and_policy
    wiki/Separation_of_concerns

http://www.gnu.org/
    fun/jokes/pasta.code.html

https://en.wikipedia.org/
    wiki/Spaghetti_code
    wiki/Spaghetti_code#Lasagna_code
    wiki/Spaghetti_code#Ravioli_code

http://www.laputan.org/mud/
    Big Ball of Mud

https://blog.codinghorror.com/
    the-big-ball-of-mud-and-other-architectural-disasters/

https://msdn.microsoft.com/
    en-us/library/dd409437.aspx

https://martinfowler.com/
    articles/designDead.html

https://en.wikipedia.org/
    wiki/4+1_architectural_view_model
    wiki/Category:Unified_Modeling_Language_diagrams

Logical         -- Classes, inheritance, composition
Development     -- Object hierarchies, connected interfaces
Physical        -- Software, hardware, networks
Process         -- Internal activities
Scenarios       -- [Use Cases]

- PlantUML (sequence diagrams) (http://plantuml.com/)
- tgif (http://bourbon.usc.edu/tgif/)

https://en.wikipedia.org/
    wiki/List_of_Unified_Modeling_Language_tools

https://www.google.com/search?q=uml+cheat+sheet


https://en.wikipedia.org/
    wiki/Software_design_pattern
    - "Gang of Four" book
    - "Python doesn't need design patterns"
    - Language features
    - Please note in comments

https://en.wikipedia.org/
    wiki/Adapter_pattern
    - Create an object containing one object
    - Change method names/parameters
      - Adapt old class to new interface
      - Adapt new class to old interface
    - Useful for refactoring

https://en.wikipedia.org/
    wiki/Facade_pattern
    - Create an object containing many objects
    - Simplified interface
    - Domain specific API
    - Divide and conquer


https://en.wikipedia.org/
    wiki/Multitier_architecture


https://en.wikipedia.org/
    wiki/Model-view-viewmodel
    wiki/Model-view-presenter


Dependency Rules

- Pyramid / DAG / Tree

- Parent to children
  - Facade / encapsulate

- Child to parent
  - OK within layer
  - Interface for higher layer

- Minimal peer knowledge
  - Coordinate via parent


Layer Responsibilities

Presentation
- Provide a Proxy
- Consumed by other components
- Consumed via loopback

Application
- Process
  - Create Managers, Components
- Service
  - Facade for Component
  - AuthZ and Accounting
  - Requests handed to Component
- Component
  - Create rest of the child objects
  - Main thread processes requests

Control
  - Facade for implementation
  - Coordinate lower pieces
  - Synchronization / Locking

Data
  - Implementation details
  - Unit Tested


UML Package = Python namespace

- control/__init__.py
  - Relative-import public classes:
    from .topframe import TopFrame

- control.py

- Syntactically valid hacks...

    class data:
        class TopFrame:
            pass


attrs: Classes Without Boilerplate

http://www.attrs.org/



lxml - XML and HTML with Python

http://lxml.de/

##
## xmlutil.py
##

from contextlib import contextmanager

from lxml import etree

def str_from_etree(node, pretty_print=True):
    return etree.tostring(node,
                          pretty_print=pretty_print,
                          method='xml',         # full document
                          encoding='unicode')   # str, not bytes.

def etree_from_str(s):
    e = etree.XML(s)
    return e

def etree_from_file(fobj):
    e = etree.parse(fobj)
    return e

def etree_from_filename(fname):
    with open(fname, 'b') as f:
        e = etree_from_file(f)
    return e

def subelement(p, tag, **attrs):
    c = etree.SubElement(p, tag, **attrs)
    return c

@contextmanager
def subcontext(p, tag, **attrs):
    c = etree.SubElement(p, tag, **attrs)
    yield c


https://en.wikipedia.org/wiki/Software_crisis

https://en.wikipedia.org/wiki/Anti-pattern

https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/

http://www.catb.org/esr/writings/taoup/html/