To start we need a file, copy paste the following into a file called input.txt that you save in the same folder as your python script.

Some comment that is not very useful
temperature: 20 
distance: 100
coordinates 1 2 3.0

Reading

To read a file we need to open it in read mode this is done with the "r" in a with open ... statement

with open("input.txt", "r") as inputFile:
  line = inputFile.readline() # this reads the first line
  print (line)
  for line in inputFile: # this reads the rest of the lines
    print(line)

At this point the variable line still contains the last line. To extract information from that line we can use the split() function

splittedLine = line.split() # check your variable explorer to see what's in splittedLine
xCoord = float(splittedLine[1])
yCoord = float(splittedLine[2])
zCoord = float(splittedLine[3])

To convert the text input to a number we need to use the float() function, if you want to convert text to an integer use int().

Suppose now that we want to store the whole file, we could run

storage = [] # create an empty list
with open("input.txt", "r") as inputFile:
  for line in inputFile: 
    storage.append(line) # append every line to the list

use your variable explorer to see what has happened.

f-strings (formatting your output)

f-strings are a very nice python feature, they allow you to print the value of variables inside strings. An f-string is just a normal string with an f in front of it, an example

pi = 3.141592653589793
integer = 5
print(f"pi has a value of {pi}")
print(f"pi has a value of {pi:10.5f}")
print(f"integer width 10: {integer:10d}")

The first print statement should be clear on its own, in the second print statement we added :10.5f this indicates that the number should be printed in a field that is 10 characters wide, should contain 5 decimal places after the dot and is a float (f), for an integer use the letter d.

Writing

To write to a file we open the file in write "w" mode

with open("output.txt", "w") as outputFile:
  for data in ["bicycle", "koala", [1,2,3], 4, 5.0]: 
    outputFile.write(f"here is the data: {data}\n")

Have a look at the output.txt to see what it did exactly. Note that if we write to a file we should specify where an “enter” should be placed, this is done with the new line symbol \n.