The Python 3 range() object doesn’t produce numbers immediately; it is a smart sequence object that produces numbers on demand. All it contains is your start, stop and step values, then as you iterate over the object the next integer is calculated each iteration. The object also implements the object.__contains__ hook, and calculates if your … Read more
datetime.strptime parses an input string in the user-specified format into a timezone-naive datetime object: >>> from datetime import datetime >>> datetime.strptime(‘Jun 1 2005 1:33PM’, ‘%b %d %Y %I:%M%p’) datetime.datetime(2005, 6, 1, 13, 33) To obtain a date object using an existing datetime object, convert it using .date(): >>> datetime.strptime(‘Jun 1 2005’, ‘%b %d %Y’).date() date(2005, … Read more
Environment variables are accessed through os.environ: import os print(os.environ[‘HOME’]) To see a list of all environment variables: print(os.environ) If a key is not present, attempting to access it will raise a KeyError. To avoid this: # Returns `None` if key doesn’t exist print(os.environ.get(‘KEY_THAT_MIGHT_EXIST’)) # Returns `default_value` if key doesn’t exist print(os.environ.get(‘KEY_THAT_MIGHT_EXIST’, default_value)) # Returns `default_value` … Read more
This somewhat depends on what platform you are on. The most common way to do this is by printing ANSI escape sequences. For a simple example, here’s some Python code from the Blender build scripts: class bcolors: HEADER = ‘\033[95m’ OKBLUE = ‘\033[94m’ OKCYAN = ‘\033[96m’ OKGREEN = ‘\033[92m’ WARNING = ‘\033[93m’ FAIL = ‘\033[91m’ … Read more
Here’s a generator that yields evenly-sized chunks: def chunks(lst, n): “””Yield successive n-sized chunks from lst.””” for i in range(0, len(lst), n): yield lst[i:i + n] import pprint pprint.pprint(list(chunks(range(10, 75), 10))) [[10, 11, 12, 13, 14, 15, 16, 17, 18, 19], [20, 21, 22, 23, 24, 25, 26, 27, 28, 29], [30, 31, 32, 33, … Read more
How do I manually throw/raise an exception in Python? Use the most specific Exception constructor that semantically fits your issue. Be specific in your message, e.g.: raise ValueError(‘A very specific bad thing happened.’) Don’t raise generic exceptions Avoid raising a generic Exception. To catch it, you’ll have to catch all other more specific exceptions that … Read more
figure tells you the call signature: from matplotlib.pyplot import figure figure(figsize=(8, 6), dpi=80) figure(figsize=(1,1)) would create an inch-by-inch image, which would be 80-by-80 pixels unless you also give a different dpi argument.
os.remove() removes a file. os.rmdir() removes an empty directory. shutil.rmtree() deletes a directory and all its contents. Path objects from the Python 3.4+ pathlib module also expose these instance methods: pathlib.Path.unlink() removes a file or symbolic link. pathlib.Path.rmdir() removes an empty directory.
super() lets you avoid referring to the base class explicitly, which can be nice. But the main advantage comes with multiple inheritance, where all sorts of fun stuff can happen. See the standard docs on super if you haven’t already. Note that the syntax changed in Python 3.0: you can just say super().__init__() instead of … Read more
If you are not into long explanations, see Paolo Bergantino’s answer. Decorator Basics Python’s functions are objects To understand decorators, you must first understand that functions are objects in Python. This has important consequences. Let’s see why with a simple example : def shout(word=”yes”): return word.capitalize()+”!” print(shout()) # outputs : ‘Yes!’ # As an object, … Read more