Create a list with initial capacity in Python
Warning: This answer is contested. See comments. Results. (evaluate each function 144 times and average the duration) Conclusion. It barely matters. Premature optimization is the root of all evil.
python
How to pass a list by reference?
Lists are already passed by reference, in that all Python names are references, and list objects are mutable. Use slice assignment instead of normal assignment. However, this isn’t a good way to write a function. You should simply return the combined list.
“Private” (implementation) class in Python
Use a single underscore prefix: This is the official Python convention for ‘internal’ symbols; “from module import *” does not import underscore-prefixed objects. Reference to the single underscore convention.
Python ‘while’ with two conditions: “and” or “or”
TLDR at bottom. First off, while loops run if the following condition is true, so must return true when simplified, for the while funtion to run The and operator returns true if both conditions are true, so the while loop will only run when it is True and True. So the following won’t run if either of the dice rolled … Read more
Unable to install boto3
Don’t use sudo in a virtual environment because it ignores the environment’s variables and therefore sudo pip refers to your global pip installation. So with your environment activated, rerun pip install boto3 but without sudo.
Normalizing a list of numbers in Python
Use : to normalize against the sum to ensure that the sum is always 1.0 (or as close to as possible). use to normalize against the maximum
Anaconda “failed to create process”
I encountered the exact same error, because my username included a space. (“C:\Users\Ben Ji”) The easiest solution is to install Anaconda to another folder in the Users-folder, e.g. public. (The same error occurs when using pip, check out https://stackoverflow.com/a/35275384/6580199)
‘module’ has no attribute ‘urlencode’
urllib has been split up in Python 3. The urllib.urlencode() function is now urllib.parse.urlencode(), the urllib.urlopen() function is now urllib.request.urlopen().
How do you switch between python 2 and 3, and vice versa?
Using ‘virtualenv’ you can have different isolated Python environments on a single machine. Also you can switch any-time between the different python interpreter versions. What is virtualenv? A Virtual Environment is an isolated working copy of Python which allows you to work on a specific project without worry of affecting other projects. It enables multiple side-by-side installations … Read more
Error loading MySQLdb module: No module named ‘MySQLdb’
MySQLdb is only for Python 2.x. You can’t install in Python 3.x versions. Now from your question i can see that you are working with Django. In this case you have three alternatives, from Django mysql notes: mysqldb mysqlclient mysql-connect-python This gives to you two alternatives, mysqlclient and mysql-connect-python, The first one requires compilation from extensions … Read more