timestable.py

I think I’m going to stick with this theme for now. It accommodates my WP-SynHighlight plugin rather well, and it’s easy to read. It’s rather plain, but that’s a sacrifice I’m willing to make.

Since I have jumbled up the appearance of my website for the sake of displaying programming code, let’s have a look at a small Python program I wrote and break it down.

# produce a multiplication table with the number of rows and columns defined by the user

columns = int(raw_input(“Input the number of columns: “))

rows = int(raw_input(“Input the number of rows: “))

longest = len(str(columns * rows)) # find out how many digits are needed for rjust() to format table evenly

for table in range (1, rows+1):

for table2 in range (1, columns+1):

result = table * table2

print str(result).rjust(longest),

print

Line 1: We begin the program with a comment. Comments in Python are set off by the # symbol. Python will ignore everything on a line after the # appears. I have been taught that adding comments and notations is important when programming. It makes the program easier to read by someone else who might be having a look, and it also helps you remember why you wrote a particular piece of code. So I am going to try to add comments and notations where appropriate. As you can see from the comment in Line 1, this program creates a multiplication table as defined by the user.

Line 2: Here we ask the user how many columns how many columns we want to appear in the multiplication table, and we assign that value to the variable “columns.” The int() means we want what’s in the following set of parentheses to be an integer. raw_input() is supposedly better than just input() because of some rare bugs. I’ve been told to use raw_input() over input() as standard practice, so that’s what I’m doing. raw_input() prints what’s in the quotes in the next set of parentheses and waits for the user to input something. If the user inputs something other than a number, the program produces and error and terminates, because of the int() function. For example, if the user inputs “ABC,” int() can’t return an integer, thus causing the error. But for now we’ll just pretend that the only thing the user would enter is a number. So because the raw_input() is inside the int(), columns ends up being an integer of whatever the user inputs.

Line 3: The same thing happens here as in Line 2, and assigns this value to the variable “rows.”

Line 4: Now we want to find out how many digits the largest number in the program will be, so we can space the table out evenly. The len() function returns the length of the string inside the parentheses. But columns * rows doesn’t produce a string, so we have to put the str() function inside the len() function. So str() returns a string representation of columns * rows, and len() returns the length of that string, and assigns it the the variable “longest.”

Line 5: Now we have all the information we need to create our table. We make a for loop called table, and give it a range of 1 through the value of “rows” + 1. We add the + 1 because the range in a for loop is exclusive on the back end, meaning it doesn’t include the actual last value of that loop.

Line 6: Inside the first loop called “table,” we make another for loop called “table2,” with the values of 1 through the value of “columns” + 1.

Line 7: Inside the table2 loop, we get the results for each cell of our multiplication table by multiplying the values of table and table2. As the program goes through the cycles of the two loops, the values of table and table2 change and give a different result for each cycle. We assign this value to the variable “result.”

Line 8: Now we print a string representation of the value of the “result” variable, and we add “.rjust(longest)” to tell Python we want it to print the result right-justified to the number of spaces in parentheses, which we get by plugging in the “longest” variable we got in Line 4. We put a comma at the end of this line to keep Python from adding a carriage return after printing the result.

Line 9: This line is moved back 4 spaces, so it’s not part of the “table2” loop. We just add a print statement here so Python now adds the carriage return after finishing a line of the multiplication table.

Now there are a couple of improvements I want to make to this program. One improvement I want to make is to have a contingency plan for when the user inputs something other than a usable number for rows or columns. That shouldn’t be too hard. Another improvement I want to make is instead of printing the multiplication table to the screen, the program will output the results to a text file, because if you make a very large multiplication table, you run out of space and the lines break over before it gets to the end.