# Getting Started

This lesson will walk you through some basic commands and operations in Python.

We'll cover the following

## Native Python for science #

Let’s see what Python looks like! I hope you know the basics of Python, but this lesson will hopefully be a good, quick refresher. The first thing you will notice is that Python makes use of whitespace and does not use a use semicolon( ;) like some other languages. Here is a very simple example:

Press + to interact
x = 5y = 10print(x+y)

### Importing functionalities #

We will make use of many libraries, some that are pre-installed with Python and some we will have to install ourselves. To get a library use an import statement:

from collections import Counter


This command imports the class Counter from the collections library. Counter is a very useful tool for data scientists; it can count the number of times items appear in collections such as lists. For example, in the code below we will create a list of marriage ages. Using Counter we can quickly count the number of times each unique age appears.

### Lists in Python #

Lists are a useful data structure to store data. They will be studied in more detail during the next lesson. For example:

Press + to interact
from collections import Countermarriage_ages = [22, 22, 25, 25, 30, 24, 26, 24, 35]  # create a listvalue_counts = Counter(marriage_ages)  # apply the counter functionalityprint(value_counts.most_common())

You can see that we created a list containing marriage ages using the [] at line 2. We then fed that list into the Counter function at line 4 to print out the most common values as a list of tuples, at line 5.

A tuple is a collection inside the (). These tuples contain two elements: the value and then the number of times that value appeared in your list. The frequency orders the list of tuples. The value with the most occurrence appears first.

### Functions in Python #

Functions are also useful. Functions in Python start with the keyword def and the function name followed by the inputs the function expects within brackets. Here is a function that takes in 2 inputs, x and y, and returns the sum:

Press + to interact
def add_two_numbers(x, y):  # function header    """    Takes in two numbers and returns the sum    parameters        x : str            first number        y : str            second number    returns        x+y    """    z = x + y    return z  # function returnprint(add_two_numbers(100,5))  # function  call

Functions can also be anonymous, meaning that you don’t have to declare them with the above structure. Instead, you can use the lambda keyword. Here is the same function as above, but as an anonymous function:

Press + to interact
y = lambda x, y: x + y  # an anonymous function which takes x and y and input and returns x+yprint(y(100,5))  # call the function

Now that you have seen the basics of Python, in the next section we will introduce the most common data structures you will need to know for data processing.