Annex: Python basics - PyPSA Workshop Birmingham

Running Python¶

There are three main ways to run Python code.

By running a Python file, e.g. python myscript.py
Through an interactive console (Python interpreter or iPython shell)
In an interactive notebook (e.g. Jupyter, .ipynb files)

Basics¶

Comments are anything that comes after the “#” symbol

a = 1  # assign integer 1 to variable a
b = "hello"  # assign string "hello" to variable b

We can print variables to see their values:

# how to we see our variables?
print(a)
print(b)

1
hello

All variables are objects. Every object has a type. To find out what type your variables are

print(type(a))
print(type(b))

<class 'int'>
<class 'str'>

Objects can have attributes and methods, which can be accessed via variable.method

# this returns the method itself
b.capitalize

<function str.capitalize()>

# this calls the method
b.capitalize()

'Hello'

Math¶

Basic arithmetic and boolean logic is part of the core Python library.

# addition / subtraction
1 + 1 - 5

-3

# multiplication
5 * 10

50

# division
1 / 2

0.5

# exponentiation
2**4

16

# rounding
round(9 / 10)

1

Comparisons¶

We can compare objects using comparison operators, and we’ll get back a boolean (i.e. True/False) result:

2 < 3

True

"energy" == "power"

False

2 != "2"

True

2 == 2.0

True

Booleans¶

We also have so-called “boolean operators” or “logical operators” which also evaluate to either True or False:

True and True

True

True and False

False

True or True

True

(not True) or (not False)

True

Conditionals¶

Conditionals allow a program to make decisions. They dictate the flow of execution based on whether certain conditions are met.

x = 100
if x > 0:
    print("Positive Number")
elif x < 0:
    print("Negative Number")
else:
    print("Zero!")

Positive Number

if x > 0:
    print("Positive Number")
    if x >= 100:
        print("Huge number!")

Positive Number
Huge number!

Loops¶

Loops tell a program to perform repetitive tasks. They govern the flow of execution by repeatedly processing a block of code, often until a certain condition is reached.

There are two types of loops: the for loop, which iterates over a sequence of values, and the while loop, which continues execution as long as a specified condition remains true.

count = 0
while count < 10:
    print(count)
    count += 1

for i in range(5):
    print(i)

for carrier in ["electricity", "hydrogen", "methane"]:
    print(carrier, len(carrier))

electricity 11
hydrogen 8
methane 7

Lists¶

list = ["electricity", "hydrogen", "methane"]

Finding out the length of a list:

len(list)

3

Joining two lists:

x = [1, 2, 3]
y = [9, 8, 7]
z = x + y
z

[1, 2, 3, 9, 8, 7]

Accessing items from a list:

z[0]

1

z[-1]

7

z[:4]

[1, 2, 3, 9]

z[-4:]

[3, 9, 8, 7]

Checking if item in list:

5 in z

False

Dictionaries¶

This is another useful data structure. It maps keys to values.

d = {
    "name": "Reuter West",
    "capacity": 564,
    "fuel": "hard coal",
}

# access a value
d["capacity"]

564

# test for the presence of a key
print("fuel" in d)

True

# add a new key
d["technology"] = "CHP"
d

{'name': 'Reuter West',
 'capacity': 564,
 'fuel': 'hard coal',
 'technology': 'CHP'}

for k, v in d.items():
    print(k, v)

name Reuter West
capacity 564
fuel hard coal
technology CHP

Now we have the building blocks we need to do basic programming in Python.

Exercises¶

Task 1: What is 5 to the power of 5?

Task 2: Create a list with the names of every planet in the solar system (in order). Have Python tell you how many planets there are in the list.

Task 3: Create a dictionary that contains the main facts about the following power plant in Berlin. Use this dictionary to access the main fuel type.

https://powerplants.vattenfall.com/reuter-west/

rw = {
    "Country": "Germany",
    "Electricity Capacity": 564,
    "Heat Capacity": 878,
    "Technology": "Combined heat and power (CHP)",
    "Main Fuel": "Hard coal",
    "Vattenfall ownership share": "100%",
    "Status": "In Operation",
}