Tag Archives: python tutorials

How to define strings in Python

A string is identified through the use of quotation marks. In the definition of a string in Python both single and double quotes can be used: “string”.

This double possibility of using the identifier allows us to include a type of quotation marks in a string enclosed by quotation marks of the other type, which is indispensable for example in the use of the apostrophe.

To better understand what has been said, let’s see an example:

>>> print “String containing the apostrophe …”

How to define strings in Python

Let’s see in detail how many ways it is possible to define a string:

  •    With single quotes: ‘String in Python!’
  •    With double quotes: “String in Python!”
  •    Escape sequences: “Type the command \” ls \ “”
  •    Through the use of transformation functions from other types of values: str (1111), str (11.11), str (11.1 + 1j)
  •    Finally the multiline strings with the adoption of three quotes (single or double).

To deep this argument:

Arithmetic operators in Python

In this post, let’s see how to perform simple calculations in the Python environment. Suppose we want to use the Python prompt as a simple calculator, then we will write:

>>> 6 + 5
11

Here we have visualized the result of an arithmetic operation: the sum of five and six. Python recognizes the numbers and the addition sign and adds them. Then show the result.

All arithmetic operators can be used:

  • addition (+)
  • subtraction (-)
  • multiplication (*)
  • division (/)

We can then combine different operations to get multiple expressions:

>>> ((5 * 4) + (6 – 3)) / (1 + 4)
4.6

In the expression we have just seen, it is possible to notice how Python uses parentheses to perform operations on numbers, these determine variations in the order in which they are performed.

Arithmetic operators in Python

Let’s see what happens if you write the same sequence without the brackets:

>>> 5 * 4 + 6 – 3/1 + 4
27.0

As you can see the result is quite different and depends on the fact that Python calculates the multiplications and divisions before the sums and subtractions, according to what is dictated by the rules imposed by the algebra.

These rules are imposed by all programming languages ​​and are used to determine the evaluation sequence of operations that goes by the name of precedence between operators.

Comments in Python

Commenting on Python is an operation that in some ways is very different from other languages, but it is quite easy to get used to this new way of inserting the explanatory text in our codes.

In Python there are basically two ways to comment on a program:

  •   single line of comment
  •   multiple line of comment

The single comment line is used to insert a short comment (or for debugging), while the multiple comment line is often used to describe something much more detailed.

Let’s see then some explanatory examples to better understand the concepts introduced up to now. Let’s start with the single line of comment:

print ("This is not a comment")
#print ("This is a comment")

Then when the interpreter encounters the symbol # (hash) ignores everything following the symbol until the end of the line. We could also write like this:

print ("This is not a comment") # Printing a text string

As for the multiple comment line instead we will use the symbol “‘, let’s see how:

" '
print ("This is not a comment")
print ("Additional comment line")
" '
print ("This is not a comment")

The comments are a useful resource for the programmer because they allow us to insert very valuable explanatory text in the optics reusability, but they are also particularly effective in the code debugging phase where the insertion of text strings helps in identifying possible bugs in our program.