12 Function tricks every Python developer should know

I am taking all the examples from the Python learning Android app called Programming Hero

12 function-related exercises/concepts:

1. Use parameter
2. Use return
3. Default parameter value
4. Keyword Arguments
5. Built-in function
6. Use docstring
7. Anonymous function
8. Access global variable
9. return more than one value
10. Variable-length argument
11. Pass by reference vs value
12. use main() function

1. Use Parameter:

Know how to declare parameters. How you can pass values to get a different result based on the parameters

def add (a, b):
    sum = a + b
    print(sum)

add(2,3)

2. Use Return:

Practice how to use the return keyword. So that you can do something with the result. If needed, you can use the result of the function again.

def add (a, b):
    return a + b

x = add(2,3)
y = add(5,10)
total = add(x,y)
print(total)

3. Default Parameter:

Learn how can you avoid passing specific parameters. If one or more parameters are not passed, you can have a default value.

def add (a, b = 5):
    return a + b

x = add(2,3)
print(x) # 5

y = add(7)
print(y) #112

total = add(x,y)
print(total)

4. Keyword Arguments

If you are not sure about the order of the parameters (arguments), you can pass arguments by their name and you don’t have to maintain their order.

def add (a, b):
    return a + b

x = add(a = 2, b =3)
print(x) # 5

y = add(b = 7, a=11)
print(y) #16

total = add(b=x,a=y)
print(total)

5. Built-in function

Python has tons of built-in function. Like min, list, pow, len, etc. Here is the list of all Built-in Functions.

6. Use docstring

Learn how would you write the purpose and special notes about a function. In that case, using docstring is a convention.

A docstring is written right after the function name. It starts with three double quotes and ends with three double quotes as well. A docstring could be written multiple lines as well.

def add (a, b):
    """ Add two numbers or two strings """
    return a + b

7. Anonymous function

An anonymous function could be considered an advanced topic. It is also known as a lambda function. It is a shortcut way to write a function in one line without giving it a proper name.

double = lambda x: x * 2
# Output: 10
print(double(5))

8. Access global variable

This tricks new developers. You can access external variables. However, if you want to set a value to a variable not declared inside the function or is not a parameter, you will get an exception.

c = 5
def add (a, b):
    c = a + b
    return c

# will get an exception
x = add(12, 23)

# use global

def add (a, b):
    global c
    c = a + b
    return c

9. return more than one value

In some cases, you will need to return more than one thing from a function. How would you do that?

The answer is: you can use a tuple, list, dictionary, class or, a dataclass.

def get_a_lot(x):
    y0 = x + 1
    y1 = x * 3
    y2 = y0 ** y3
    return (y0, y1, y2)

things = get_a_lot(5)

10. Variable-length argument

In some cases, you might not know, how many parameters user will pass. In those cases, what will you do?

def add_everything(*args):
    return sum(args)

# Calculate the sum
print(add_everything(1,4,5, 75, 112))

11. Mutable Vs Immutable parameters

This is an advanced topic. However, you should check when you pass a variable, list, tuples or a dictionary to a function. What will happen if you change the value and what will happen if you just update one element of the collection?

If you are not sure, read the comment below by Jason.

12. use main() function

The main function has special importance to start an app. You should learn about this.

# Define `main()` function
def main():
  hello()
  print("This is a main function")

# Execute `main()` function 
if __name__ == '__main__':
    main()

If you read up to this point, you should check out the intermediate and advanced level contents in Programming Hero

Comments

[Jason C. McDonald]

1. Pass by reference vs value

Python does neither. It has names which are bound to values. Values can be either mutable or immutable. This isn't really advanced, so much as unusual, but it is very important to understand when working in Python!

So, in...

answer = 42
insight = answer
insight = 4

...the name answer is bound to the value 42. insight is initially bound to the same value that answer is (names cannot be bound to other names). On the third line, insight is rebound to the value 4.

The behavior you're referring to is actually related to whether the data type being passed is mutable or immutable.

Immutable types seem to behave like pass-by-value because the value cannot be modified.

def increment(num):
    num = num + 1
    return num

spam = 5
eggs = increment(spam)
print(spam)  # 5
print(eggs)  # 6

In that example, foo is passed to increment(), so the parameter num gets bound to the same value as foo. This is identical to num = foo, by the way. However, an integer is immutable, meaning that value cannot be modified. So, num = num + 1 actually rebinds to a new value, 6, which is returned and bound to eggs.

Mutable data types, on the other hand, seem to behave like "pass-by-reference"...

def append_sum(numbers):
    numbers.append(sum(numbers))
    return numbers

spam = [1, 2]
eggs = append_sum(spam)

print(spam)  # [1, 2, 3]
print(eggs)  # [1, 2, 3]

Lists are mutable. Again, when we pass spam to the function, it's the same as if we said numbers = spam; numbers is now bound to the same value as spam. However, because that value is mutable, it can be changed directly, which we do with our numbers.append() call. Because both spam and numbers are still bound to the exact same value in memory, both see the mutation.

Then, when we return numbers, we wind up binding that same value to eggs as well. Thus, spam and eggs are (again) bound to the exact same value in memory.

Common immutable data types:

• bool: True, False
• str (string): "Hello, world!"
• int, float, complex
• tuple: (1, 2, 3)
• bytes
• frozenset

Common mutable data types:

• list: [1, 2, 3]
• set: {1, 2, 3}
• dict (dictionary): {1: 'a', 2: 'b', 3: 'c'}
• (Most objects)

Dead Simple Python: Data Typing and Immutability

Jason C. McDonald ・ Jan 17 '19 ・ 19 min read

#python #beginners #coding

Also watch Ned Batchelder's excellent talk on this topic.

[JS Dude]

WOW. Well explained. Thanks, Jason