Checking if a dictionary is empty
boolwill return false ifdictis empty- but wait, there's more! no need to explicitly
boolcast if the object is a collection (list, dict, set, set, etc)
What's with the with statement
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It’s handy when you have two related operations which you’d like to execute as a pair, with a block of code in between. The classic example is opening a file, manipulating the file, then closing it
with open('output.txt', 'w') as f: f.write('Hi there!') -
The above with statement will automatically close the file after the nested block of code. The advantage of using a with statement is that it is guaranteed to close the file no matter how the nested block exits. If an exception occurs before the end of the block, it will close the file before the exception is caught by an outer exception handler. If the nested block were to contain a return statement, or a continue or break statement, the with statement would automatically close the file in those cases, too.
Keyword Argument Gotchas
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Parameter defaults are only executed a single time: when the function is defined. Default argument values are evaluated only once per module load, which usually happens when a program starts up. After the module containing this code is loaded, the default argument will never be evaluated again.
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For strings, you can specify them as defaults in the argument list
def table_key_mapper(key_type, table_name, country='ca', stage='dev'): -
The above is only true for default argument values that are immutable (such as strings). If you try and do this with a list, e.g.
def table_key_mapper(some_arg=[1,2,3]), you're gonna have a bad time due to how Python evaluates default values at compile/load time vs. runtime, which means mutable values such as lists or dictionaries are a no-no.
Testing in Flask
- This was first discovered when the
gglobal object was not attaching a specific property to itself in abefore_requesthandler. - The solution to the above problem can be found here in the Flask Docs
v3.0