0x00-python_variable_annotations

Python - Variable Annotations

The learning objectives of this project are:

• Type annotations in Python 3
• How you can use type annotations to specify function signatures and variable types
• Duck typing
• How to validate your code with mypy

0. Basic annotations - add

Write a type-annotated function add that takes a float a and a float b as arguments and returns their sum as a float.

1. Basic annotations - concat

Write a type-annotated function concat that takes a string str1 and a string str2 as arguments and returns a concatenated string

2. Basic annotations - floor

Write a type-annotated function floor which takes a float n as argument and returns the floor of the float.

3. Basic annotations - to string

Write a type-annotated function to_str that takes a float n as argument and returns the string representation of the float.

4. Define variables

Define and annotate the following variables with the specified values:

• a, an integer with a value of 1
• pi, a float with a value of 3.14
• i_understand_annotations, a boolean with a value of True
• school, a string with a value of “Holberton”

5. Complex types - list of floats

Write a type-annotated function sum_list which takes a list input_list of floats as argument and returns their sum as a float.

6. Complex types - mixed list

Write a type-annotated function sum_mixed_list which takes a list mxd_lst of integers and floats and returns their sum as a float.

7. Complex types - string and int/float to tuple

Write a type-annotated function to_kv that takes a string k and an int OR float v as arguments and returns a tuple. The first element of the tuple is the string k. The second element is the square of the int/float v and should be annotated as a float.

8. Complex types - functions

Write a type-annotated function make_multiplier that takes a float multiplier as argument and returns a function that multiplies a float by multiplier.

9. Let's duck type an iterable object

Annotate the below function’s parameters and return values with the appropriate types

def element_length(lst):
    return [(i, len(i)) for i in lst]

10. Duck typing - first element of a sequence

Augment the following code with the correct duck-typed annotations:

# The types of the elements of the input are not know
def safe_first_element(lst):
    if lst:
        return lst[0]
    else:
        return None

11. More involved type annotations

Given the parameters and the return values, add type annotations to the function

Hint: look into TypeVar

def safely_get_value(dct, key, default = None):
    if key in dct:
        return dct[key]
    else:
        return default

12. Type Checking

Use mypy to validate the following piece of code and apply any necessary changes.

def zoom_array(lst: Tuple, factor: int = 2) -> Tuple:
    zoomed_in: Tuple = [
        item for item in lst
        for i in range(factor)
    ]
    return zoomed_in


array = [12, 72, 91]

zoom_2x = zoom_array(array)

zoom_3x = zoom_array(array, 3.0)