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% Document Info
\author{sercand}
\pdfinfo{
  /Title (python-design-patterns.pdf)
  /Creator (Cheatography)
  /Author (sercand)
  /Subject (Python Design Patterns Cheat Sheet)
}

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\fancyhead[L]{
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{C}
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    \vspace{-7pt}
    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
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    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Python Design Patterns Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{sercand} via \textcolor{DarkBackground}{\uline{cheatography.com/32560/cs/10035/}}}
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\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{LL}
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  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}sercand \\
  \uline{cheatography.com/sercand} \\
  \end{tabulary}
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\begin{tabulary}{5.8cm}{L}
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  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Published 2nd December, 2016.\\
   Updated 2nd December, 2016.\\
   Page {\thepage} of \pageref{LastPage}.
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  Measure your website readability!\\
  www.readability-score.com
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\begin{document}
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\begin{multicols*}{3}

\begin{tabularx}{5.377cm}{X}
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\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Singleton}}  \tn
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{def Singleton(cls): \newline   \_instances = \{\}  \newline   def getinstance(): \newline     if cls not in \_instances: \newline       \_instances{[}cls{]} = cls() \newline     return \_instances{[}cls{]} \newline   return getinstance \newline  \newline @Singleton \newline class Counter(object): \newline   def \_\_init(self): \newline     if not hasattr(self ,'val'): self.val = 0 \newline   def get(self): return self.val \newline   def incr(self): self.val += 1} \tn 
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\mymulticolumn{1}{x{5.377cm}}{@Singleton \newline class PlayerFactory(object): \newline   def new(self, name, type):  \newline     if type == 'peasant': \newline       return Peasant(name)  \newline     elif type == 'warior': \newline       return Warior(name)  \newline     return None} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\par\addvspace{1.3em}

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\mymulticolumn{1}{x{5.377cm}}{class CounterProxy(object): \newline     def \_\_init\_\_(self, type): \newline         self.type = type \newline     def incr(self): \newline         if self.type == 'W': \newline             Counter().incr() \newline     def get(self): \newline         Counter().get()} \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}-}
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\par\addvspace{1.3em}

\begin{tabularx}{5.377cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Producer}}  \tn
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{5.377cm}}{class Producer(Thread): \newline  \newline   def \_\_init\_\_(self, queue, cvs, maxsize=5): \newline     \seqsplit{Thread.\_\_init\_\_(self)} \newline     self.queue = queue \newline     self.maxsize = maxsize \newline     self.notfull = cvs{[}0{]} \newline     self.notempty = cvs{[}1{]} \newline     self.terminate = False \newline     self.counter = 0 \newline  \newline   def run(self): \newline     while not self.terminate: \newline       sleep(0.1 * randint(0, 10))  \# sleep randomly \newline  \newline       self.notfull.acquire() \newline       while len(self.queue) \textgreater{}= self.maxsize:  \# full \newline         print "full queue, waiting" \newline         self.notfull.wait() \newline         if self.terminate: \newline           break \newline       self.notfull.release() \newline       self.counter += 1 \newline       \seqsplit{self.queue.append(self.counter)} \newline       self.notempty.acquire() \newline       self.notempty.notify()  \# notify consumer, a new item \newline       self.notempty.release() \newline  \newline   def quit(self): \newline     self.terminate = True \newline     self.notfull.acquire() \newline     self.notfull.notify() \newline     self.notfull.release()} \tn 
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\mymulticolumn{1}{x{5.377cm}}{class Subject(object): \newline     \_observers = {[}{]} \newline     def register(self, obs): \newline         \seqsplit{self.\_observers.append(obs)} \newline     def unregister(self, obs): \newline         \seqsplit{self.\_observers.remove(obs)} \newline     def notify(self): \newline         for o in self.\_observers: \newline             o.update(self) \newline     def state(self): pass \newline class Observer(object): \newline     def update(self, subj): pass \newline class Clock(Subject): \newline     def \_\_init\_\_(self): \newline         self.value = 0 \newline     def state(self): \newline         return self.value \newline     def tick(self): \newline         self.value += 1 \newline         self.notify() \newline class Person(Observer): \newline     def update(self, obj): \newline         print "heyo", obj.state() \newline a = Person() \newline b = Clock() \newline b.register(a) \newline b.tick()} \tn 
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\mymulticolumn{1}{x{5.377cm}}{class AuthFacade(object): \newline     def \_\_init\_\_(self ,method):  \newline         if method == 'passwd': \newline             \# \newline         elif method =='oauth': \newline             \# \newline         elif method =='otp': \newline             \#  \newline         else: \newline                 throw ... \newline     def auth(self,identity,data): \newline         \#check authentication based on setting} \tn 
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\begin{tabularx}{5.377cm}{X}
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\mymulticolumn{1}{x{5.377cm}}{\bf\textcolor{white}{Consumer}}  \tn
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\mymulticolumn{1}{x{5.377cm}}{class Consumer(Thread): \newline   def \_\_init\_\_(self, queue, cvs): \newline     \seqsplit{Thread.\_\_init\_\_(self)} \newline     self.queue = queue \newline     self.notfull = cvs{[}0{]} \newline     self.notempty = cvs{[}1{]} \newline     self.terminate = False \newline   def run(self): \newline     while not self.terminate: \newline       sleep(0.1 * randint(0, 10))  \# sleep randomly \newline       self.notempty.acquire() \newline       while len(self.queue) == 0:  \# empty \newline         print "empty queue, waiting" \newline         self.notempty.wait() \newline         if self.terminate: \newline           break \newline       self.notempty.release() \newline       item = self.queue{[}0{]} \newline       del self.queue{[}0{]} \newline       print "consumed ", item \newline       self.notfull.acquire() \newline       self.notfull.notify()  \# notify consumer, a new item \newline       self.notfull.release() \newline   def quit(self): \newline     self.terminate = True \newline     self.notempty.acquire() \newline     self.notempty.notify() \newline     self.notempty.release()} \tn 
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\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{patterns}}  \tn
% Row 0
\SetRowColor{LightBackground}
A complex library, tool or system; consisting of many functions and/or classes; probably poorly designed is tried to be accessed. It is hard to read and understand. There are many dependencies distributed in the source, needs many housekeeping tasks and stages to access. Any change in the system require changes in the whole source code. & Facade:Define a class implementing all details of the library/system and providing a simple uniform interface. Access the library through this interface. \tn 
% Row Count 17 (+ 17)
% Row 1
\SetRowColor{white}
You need to access a hard to duplicate, limited, probably old class definition. You donot have a chance to improve it or change the interface. Or, you want to have restricted access to methods (authorization). Or, you want smarter access like caching. & Proxy: Write a class interface implementing functionalities missing in the original interface. \tn 
% Row Count 30 (+ 13)
\end{tabularx}
\par\addvspace{1.3em}

\vfill
\columnbreak
\begin{tabularx}{5.377cm}{x{2.4885 cm} x{2.4885 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{5.377cm}}{\bf\textcolor{white}{patterns (cont)}}  \tn
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\SetRowColor{LightBackground}
Objects depending on eachothers states need to be informed when the other encountered a change. Event handling systems. & Observer: Maintain a registry of observing objects in Subject object. When an event occurs, notify the observers. \tn 
% Row Count 6 (+ 6)
% Row 3
\SetRowColor{white}
Create objects from a set of classes. Implementation depends on class definitions. Introduction of new classes and other changes need recompilation. Class constructors exposed. & Factory: Use interface functions/objects to encapsulate class names and constructors. Use a interface functions, methods to provide you instances. Rest is handled by polymorphism. \tn 
% Row Count 15 (+ 9)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}