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When Pythons Attack. When Pythons Attack Pages: 1, 2 Programming Mistakes Finally, here are some of the problems you may come across when you start working with the larger features of the Python language -- datatypes, functions, modules, classes, and the like. Because of space constraints, this section is abbreviated, especially with respect to advanced programming concepts; for the rest of the story, see the tips and "gotchas" sections of Learning Python, 2nd Edition. File-Open Calls Do Not Use the Module Search Path When you use the open() call in Python to access an external file, Python does not use the module search path to locate the target file.
It uses an absolute path you give, or assumes the filename is relative to the current working directory. Methods Are Specific to Types You can't use list methods on strings, and vice versa. Immutable Types Can't Be Changed in Place Remember that you can't change an immutable object (e.g., tuple, string) in place: T = (1, 2, 3) T[2] = 4 # Error. When Pythons Attack.
10 Most Common Python Mistakes. About Python Python is an interpreted, object-oriented, high-level programming language with dynamic semantics. Its high-level built in data structures, combined with dynamic typing and dynamic binding, make it very attractive for Rapid Application Development, as well as for use as a scripting or glue language to connect existing components or services.
Python supports modules and packages, thereby encouraging program modularity and code reuse. About this article Python’s simple, easy-to-learn syntax can mislead Python developers – especially those who are newer to the language – into missing some of its subtleties and underestimating the power of the diverse Python language. With that in mind, this article presents a “top 10” list of somewhat subtle, harder-to-catch mistakes that can bite even some more advanced Python developers in the rear. Common Mistake #1: Misusing expressions as defaults for function arguments But let’s look at what actually happens when you do this: Huh? Makes sense. The Most Diabolical Python Antipattern. The following is a guest post by Aaron Maxwell, author of the Advanced Python Newsletter. There are plenty of ways to write bad code. But in Python, one in particular reigns as king. We were exhausted, yet jubilant. After two other engineers had tried for three days each to fix a mysterious Unicode bug before giving up in vain, I finally isolated the cause after a mere day’s work.
And ten minutes later, we had a candidate fix. The tragedy is that we could have skipped the seven days and gone straight to the ten minutes. But I’m getting ahead of myself… Here’s the punchline. There are variants that amount to the same thing – saying “except Exception:” or “except Exception as e:”, for example. Why do I claim this is the most diabolical anti-pattern in the Python world today? People do this because they expect a specific error to happen there. Why Do We Do This To Ourselves? Insidiously, to catch Exception then silently continue doesn’t seem like all that horrible an idea in the moment. Data animations with Python and MoviePy - __del__( self ) Python has some great data visualization librairies, but few can render GIFs or video animations. This post shows how to use MoviePy as a generic animation plugin for any other library. MoviePy lets you define custom animations with a function make_frame(t), which returns the video frame corresponding to time t (in seconds): In previous posts I used this method to animate vector graphics (with the library Gizeh), and ray-traced 3D scenes (generated by POV-Ray).
This post covers the scientific libraries Mayavi, Vispy, Matplotlib, Numpy, and Scikit-image. Animations with Mayavi Mayavi is a Python module for interactive 3D data visualization with a simple interface. Another example with a wireframe mesh whose coordinates and view angle depend on the time : As Mayavi relies on the powerful ITK visualization engine it can also process complex datasets. Animations with Vispy Vispy is another interactive 3D data visualization library, based on OpenGL. Animations with Matplotlib Animations with Numpy.
Kindling projects page. Boston Python Puzzles. Fluent interface. A fluent interface is normally implemented by using method cascading (concretely method chaining) to relay the instruction context of a subsequent call (but a fluent interface entails more than just method chaining [1]). Generally, the context is defined through the return value of a called methodself-referential, where the new context is equivalent to the last contextterminated through the return of a void context. The first two points correspond to the unit of a monadthe fact that a monad is an endofunctor while the method chaining is the binding operation. History[edit] Examples[edit] JavaScript[edit] There are many examples of JS libraries that use some variant of this: jQuery probably being the most well known. A simple way to do this in javascript is using prototype inheritance and `this`. A more general way to do this is implemented in mu-ffsm.
Java[edit] The jOOQ library models SQL as a fluent API in Java String[] datesStr = new String[] {"12-10-1492", "06-12-1978"}; ... One can write: Online Python Tutor - Learn programming by visualizing code execution. 5. Iterators & Generators — Python Practice Book. 8 Interesting Python Tricks. 1. Emulating "? :" Python doesn't know the trinary operator "? :" from C.
However, it's pretty easy to emulate: x ? (If you're sure that x is already a boolean type (or an integer of value 0 or 1), you can omit the bool() function, of course.) How does the trick work? Note that always all three operands will be evaluated, unlike the "? Actually, there's another way to do it with shortcut evaluation, but it only works if y does not contain a boolean False equivalent: x ? 2. You will often find yourself using features that are not available in older versions of Python. Import sys if not hasattr(sys, "hexversion") or sys.hexversion < 0x020300f0: sys.stderr.write("Sorry, your Python is too old. Those lines should be at the very top of your program, even before any other import statements. 3. The "cgitb" module (available since Python 2.2) is extremely helpful when debugging CGI programs. Import cgitb; cgitb.enable() 4. Tuple1, tuple2 = zip(*data) 5. 6. 7. Debug = False really = True verbose = False.
Scapy. Why Every Language Needs Its Underscore - Hackflow. (This is an adaptation of a talk I gave at PyCon and DevDay. Slides and video are available in russian) Do you know what underscore is? In its most general it’s a JavaScript library that makes life better. For whoever writes in JavaScript. I mostly write Python and I also wanted my life better, so I went ahead and wrote a similar library for Python. But the thing is you need to understand a magic behind something to properly replicate it. So what’s the magic behind _? The problem To answer this question we should look at problems this kind of libraries solve. A piece of entangled code This messy piece of code was taken from a real project and slightly simplified: There are several things entangled in here, but my point is that this could be written much shorter: If it seems hard at first, then it’s okay. Dirty dictionary But let’s go on and clean some dirty dictionary: Here we go through dictionary and clean its values by coercing them to int.
And it’s entirely possible with funcy. Wrap-up. Anti-Patterns in Python Programming - Constantine Lignos. This page is a collection of the most unfortunate but occasionally subtle issues I've seen in code written by students new to writing Python. It's written to help students get past the phase of writing ugly Python code and understand some of the most common idioms. The simplifications employed (for example, ignoring generators and the power of itertools when talking about iteration) reflect its intended audience.
There are always reasons to use some of these anti-patterns, which I've tried to give those where possible, but in general using these anti-patterns makes for less readable, more buggy, and less Pythonic code. If you're looking for broader introductory materials for Python, I highly recommend The Python Tutorial or Dive into Python. If you have comments or wish to use this work in way other than what the license allows, feel free to get in touch with me by e-mail. The use of range for i in range(len(alist)): print alist[i] for item in alist: print item Why do this? Loops. Crossplatform Framework for NUI.