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Python miscellanea

__call__

Defining __call__ let’s us use an object like a function (i.e. it’s callable).

class Adder:
    def __init__(self, n):
        self.n = n

    def __call__(self, x):
        return self.n + x

add5 = Adder(5)
print(add5(10)) # 15

globals()

The globals() function returns a dictionary representing the current global symbol table. This includes all global variables and functions in the current module.

x = 1
def foo():
    print("hello")

# Get dictionary of global symbols
global_dict = globals()
print(global_dict['x'])  # prints: 1
print(global_dict['foo'])  # prints: <function foo at ...>

You can also modify global variables using this dictionary, though this is generally not recommended:

globals()['x'] = 100
print(x)  # prints: 100

function parameters

sums(a=1234, b=5678)

is the same as

sums(**{'a': 1234, 'b': 5678})

expression vs statement

Using if as an expression rather than a statement allows us to use it inside functions. It is called a ternary operator.

def f():
    return matches if matches else 0

truthy and falsy values

In Python, 0, None, [], {}, "", () are all considered falsy.

A list with more than 0 elements, a string with more than 0 characters, a dictionary with more than 0 keys, a set with more than 0 elements, etc. are all considered truthy.
Also an integer that is not 0 is considered truthy.