Rainfall collector

w = [[x for columns in range(y)] for rows in range(z)]

In this example, w is declared as a 2D array of y columns and z rows with each element assigned to be x.

x could be a number or a string. Typically to create an empty table, x would be the empty string "".

Although columns and rows are used as variables to make the code easy to read, this is an abstraction. How you visualise the table is up to you.

You could define a 2D list where the number of elements is unknown and can change, but you cannot refer to a specific index until it contains data.

Reading CSV files

Data can be stored in comma separated file (CSV) format, where each row (record) has data separated into columns (fields) by commas.

If the number of rows and columns is known, you can use a 2D array initialised with two for loops as shown above. If the number of rows is not known, a 2D list will be needed with new rows added to the list as they are read from the file.

This is a common operation when using files and 2D lists. Here is some boilerplate code that can be used to read data from a file and return it in a 2D list called database.

# Read data from filename and return a 2D list

def read_file(filename):

database = []

file = open(filename, "r")

# Read each line of data until end of file

for record in file:

record = record.strip()

fields = record.split(",")

database.append(fields)

file.close()

return database