Python Basics¶

NOTE: This is not a comprehensive guide to writing Python code! We’ve only put the basics that would be useful in the context of an AguaClara research report. To continue learning Python, review these External Resources.

How this tutorial works¶

Some code examples will look like this:

>>> print('Hydrate or diedrate')
Hydrate or diedrate

The triple greater-than symbols >>> indicate that that line of Python code is being run in the interactive Python interpreter in the command line. The next line is what that line of Python code would output.

The interactive Python interpreter is explained in Running Python in the Command Line.

Basic Operations¶

Printing¶

>>> print('You can keep strings in single quotes,')
You can keep strings in single quotes,
>>> print("or double quotes!")
or double quotes!

Comments¶

print('This code will run,') # but this will not.

"""
Here's a
block comment!
"""

Math¶

>>> 5 + 2
7
>>> 5 - 2
3
>>> 5 * 2
10
>>> 5 / 2 # Dividing integers will round floats (decimals) down.
2
>>> 5.0 / 2.0 # Dividing floats will return floats.
2.5
>>> 5 ** 2 # Exponentiation
25
>>> 5 % 2 # Modulo
1
>>> (5 + 2) * 5 + 2 # PEMDAS
37

Logic¶

>>> True and False # Note that all of these words are case-sensitive.
False
>>> False or True
True
# Visit here for more on and/or: https://bit.ly/2vA64pM

>>> 5 == 5
True
>>> 5 == 2
False

>>> 5 != 5
False
>>> 5 != 2
True

>>> 5 > 2
True
>>> 5 < 2
False
>>> 5 <= 5
True
>>> 5 >= 5
True

Data Structures¶

Variables¶

>>> a_variable = 'can store a string'
>>> an_integer = 5
>>> a_float = 2.0
>>> a_boolean = True

>>> an_integer + a_float
7.0

Lists¶

>>> a_list = ['can store anything!', 5, 2.0, True]

>>> a_list
['can store anything!', 5, 2.0, True]
>>> a_list[0] # returns 0th (first) element
can store anything!
>>> a_list[-2] # returns 2nd to last element
2.0
>>> a_list[1:4] # list slice: returns list of elements 1 through (4-1)
[5, 2.0, True]

>>> a_list.append('add an entry to the end')
>>> a_list
['can store anything!', 5, 2.0, True, 'add an entry to the end']

>>> a_list.pop() # get and remove an entry from the end
'add an entry to the end'
>>> a_list
['can store anything!', 5, 2.0, True]

>>> a_list[0] = 'change an entry'
>>> a_list
['change an entry', 5, 2.0, True]

>>> len(a_list) # length of list
4

Dictionaries¶

>>> a_dict = {'key': 'value', 'integer': 5, 'float': 2.0, 'boolean': True} # Think of a real-life dictionary. word: definition

>>> a_dict
{'key': 'value', 'integer': 5, 'float': 2.0, 'boolean': True}
>>> a_dict['key']
value
>>> a_dict['integer']
5

>>> a_dict['key'] = 'change an entry'
>>> a_dict
{'key': 'change an entry', 'integer': 5, 'float': 2.0, 'boolean': True}

Conditional Statements and Loops¶

For this section, pay attention to the indentation of each line! Each indent must be 4 spaces or a tab.

`if elif else`¶

>>> x = 10
>>> if(x > 10):
...     print('x is greater than 10.')
... elif(x < 10):
...     print('x is less than 10.')
... else:
...     print('x is exactly 10.')
... # elif and else are optional.
x is exactly 10.

# What if x was something different?

>>> x = 8
>>> # Pretend the if-elif-else statement is here.
x is less than 10.

>>> x = 12
>>> # Pretend the if-elif-else statement is here.
x is greater than 10.

`for`¶

>>> hydraulic_processes = ['flocculation', 'sedimentation', 'filtration']
>>> for process in hydraulic_processes:
...     print(process)
... # "process" can be replaced with any word, and "hydraulic_processes" can be any list.
flocculation
sedimentation
filtration

>>> for i in range(3):
...     print(i)
... # range() starts from 0 and counts up. Note that 3 isn't printed.
0
1
2

>>> for i in range(4, 8):
...     print(i)
... # You can also set which number range() starts from.
4
5
6
7

`while`¶

>>> x = 0
>>> while x < 3:
...     print(str(x) + ' is less than 3.') # str() lets you attach numbers to strings.
...     x += 1 # Shorthand for adding 1 to x (or x = x + 1).
...
0 is less than 3.
1 is less than 3.
2 is less than 3.

Nesting¶

>>> for i in range(1, 5):
...     if i % 2 == 1: # If the remainder of i/2 is 1
...         print(str(i) + 'is odd.')
...     else:
...         print(str(i) + 'is even.')
... # Pay attention to indents when nesting statements inside of others!
1 is odd.
2 is even.
3 is odd.
4 is even.

Functions¶

>>> def exp(base, exponent):
...     return base ** exponent

>>> exp(5, 2)
25
>>> exp(2, 4) + exp(10, 2)
116
>>> print('The volume of the cube is ' + str(exp(3, 3)) + ' inches.')
The volume of the cube is 27 inches.

>>> def parity(number):
...     if number % 2 == 1:
...         print(str(number) + 'is odd.')
...     else:
...         print(str(number) + 'is even.')

>>> parity(27)
27 is odd.
>>> parity(40)
40 is even.

Now, complete Interactive Tutorial 2: Python Basics here.