Learn Python: Syntax

Get started with Python syntax in this lesson and then create a point of sale system for a furniture store!

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Key Concepts

Review core concepts you need to learn to master this subject

Comments

# Comment on a single line user = "JDoe" # End of line comment after code

A comment is a piece of text within a program that is NOT executed as part of the program. Comments can be used to provide additional information to aid in understanding the code. A comment can appear at the start of a line or at the end of a line after a piece of code. A comment is started by the # character and continues until the end of the line. It is NOT possible to include code after a comment is started.

Python Comments

# Comment on a single line user = "JDoe" # End of line comment after code

A comment is a piece of text within a program that is NOT executed as part of the program. Comments can be used to provide additional information to aid in understanding the code. A comment can appear at the start of a line or at the end of a line after a piece of code. A comment is started by the # character and continues until the end of the line. It is NOT possible to include code after a comment is started.

Python print() Function

# Comment on a single line user = "JDoe" # End of line comment after code

The print() function is used to output text, numbers, or other printable information to the console. The print() function takes one or more parameters and will output those to the console. The parameters may be string or numeric literal values, variables, or the results returned from functions. If no parameters are provided, the print() function will output a blank line.

Strings

# Comment on a single line user = "JDoe" # End of line comment after code

A string is a sequence of characters (letters, numbers, whitespace or punctuation) enclosed by quotation marks. A Python string can be enclosed using either the double quotation mark " or the single quotation mark '. If a string has to be broken into multiple lines, the backslash character \ can be used to indicate that the string continues on the next line.

Python Strings

# Comment on a single line user = "JDoe" # End of line comment after code

A string is a sequence of characters (letters, numbers, whitespace or punctuation) enclosed by quotation marks. A Python string can be enclosed using either the double quotation mark " or the single quotation mark '. If a string has to be broken into multiple lines, the backslash character \ can be used to indicate that the string continues on the next line.

Variables

# Comment on a single line user = "JDoe" # End of line comment after code

A variable is used to store data to be used by the program. This data can be a number, a string, a Boolean, a list or some other data type. Every variable has a name which can consist of letters, numbers, and the underscore character (_). No other type of characters can be used to create the variable name and the variable may NOT start with a number. The equal sign = is used to assign a value to a variable. That assignment can be from a fixed value or taken from another existing variable. It can also be used to change the value of a variable from one value to another after the initial assignment is made.

Python Variables

# Comment on a single line user = "JDoe" # End of line comment after code

A variable is used to store data to be used by the program. This data can be a number, a string, a Boolean, a list or some other data type. Every variable has a name which can consist of letters, numbers, and the underscore character (_). No other type of characters can be used to create the variable name and the variable may NOT start with a number. The equal sign = is used to assign a value to a variable. That assignment can be from a fixed value or taken from another existing variable. It can also be used to change the value of a variable from one value to another after the initial assignment is made.

Error Notification

# Comment on a single line user = "JDoe" # End of line comment after code

The Python interpreter will report errors present in your code. For most error cases, the interpreter will display the line of code and then immediately below the code, display a line with the caret character ^ under the portion of the code where the error was detected.

SyntaxError

# Comment on a single line user = "JDoe" # End of line comment after code

A SyntaxError is reported by the Python interpreter when some portion of the code is incorrect. This can include misspelled keywords, missing or too many brackets or parentheses, incorrect operators, missing or too many quotation marks, or other conditions. The Python interpreter will display the line of code where the SyntaxError was detected and place a caret (^) character under the point in the line where the interpreter believes the error exists.

Python SyntaxError

# Comment on a single line user = "JDoe" # End of line comment after code

A SyntaxError is reported by the Python interpreter when some portion of the code is incorrect. This can include misspelled keywords, missing or too many brackets or parenthesis, incorrect operators, missing or too many quotation marks, or other conditions. The Python interpreter will display the line of code where the SyntaxError was detected and place a caret character under the point in the line where the interpreter believes the error exists.

NameError

# Comment on a single line user = "JDoe" # End of line comment after code

A NameError is reported by the Python interpreter when it detects what it believes to be a variable that is unknown. This can occur is a variable is used before it has been assigned a value or if the variable name is spelled differently than the point at which it was defined. The Python interpreter will display the line of code where the NameError was detected and indicate which name it found which was not defined.

Python NameError

# Comment on a single line user = "JDoe" # End of line comment after code

A NameError is reported by the Python interpreter when it detects what it believes to be a variable that is unknown. This can occur is a variable is used before it has been assigned a value or if the variable name is spelled differently than the point at which it was defined. The Python interpreter will display the line of code where the NameError was detected and indicate which name it found which was not defined.

Division By Zero Error

# Comment on a single line user = "JDoe" # End of line comment after code

A ZeroDivisionError is reported by the Python interpreter when it detects a division operation is being performed and the denominator (bottom number) is 0. In mathematics, dividing a number by zero has no defined value, so Python treats this as an error condition and will report a ZeroDivisionError and display the line of code where the division occurred. This does not only happen when a 0 is specifically written in the code. This can also happen if a variable is used as the denominator and its value has been set to or changed to 0. In general, it is good practice to test the value of a variable before attempting to divide another number or variable with it.

Python Integers

# Comment on a single line user = "JDoe" # End of line comment after code

Python variables can be assigned different types of data. One supported data type is the integer. An integer is a number which can be written without a fractional part (no decimal). An integer can be a positive number, a negative number or the number 0 so long as there is no decimal portion. The number 0 represents an integer value but the same number written as 0.0 would represent a floating point number.

Floating Point Numbers

# Comment on a single line user = "JDoe" # End of line comment after code

Python variables can be assigned different types of data. One supported data type is the floating point number. A floating point number is a value which contains a decimal portion. Floating point numbers are used to represent numbers which have fractional quantities. For example, a = 3/5 can not be represented as an integer so the variable a is assigned the floating point value 0.6.

Python Arithmetic Operations

# Comment on a single line user = "JDoe" # End of line comment after code

Python supports different types of arithmetic operations. These operations can be performed on literal numbers, variables, or a combination of both. The primary arithmetic operators in Python are:

  • +for the addition operator
  • - for the subtraction operator
  • / for the division operator
  • * for the multiplication operator

The operator is placed between two numbers or variables and the results of the operation can be assigned to a new variable or used as the parameter for a function call.

Python Integer Division

# Comment on a single line user = "JDoe" # End of line comment after code

Python 3 will automatically convert integer numbers to floating-point before performing division. This behavior is changed from Python 2 where integer numbers were NOT automatically converted. In Python 2, use of the float() function or a literal floating point value was required to force division to produce a floating point result.

Exponentiation

# Comment on a single line user = "JDoe" # End of line comment after code

In addition to the basic operations of addition, subtraction, multiplication and division, Python supports an operator for exponentiation. That operator is written with two asterisks like so **. The format for exponentiation in Python is a number or variable followed by the operator ** followed by a number or variable which represents the power to raise the number. Both the number and the power can be floating point values.

Modulo Operator

# Comment on a single line user = "JDoe" # End of line comment after code

Python supports an operator to perform the modulo calculation. A modulo calculation returns the remainder of a division between the first and second number. For example, the result of the expression 4 % 2 would result in the value 0 because 4 is evenly divisible by 2 leaving no remainder. The result of the expression 7 % 3 would return 1 because 7 is NOT evenly divisible by 3 leaving a remainder.

Python String Concatenation

# Comment on a single line user = "JDoe" # End of line comment after code

Python supports the joining (concatenation) of strings together using the + operator. The + operator is also used for mathematical addition operations. If the parameters passed to the + operator are strings, then concatenation will be performed. If one of the parameters is NOT a string, then Python will report an error condition. Multiple variables or literal strings can be joined together using the + operator. The concatenation process does not add any whitespace between the strings that are joined.

Plus-Equals Operator

# Comment on a single line user = "JDoe" # End of line comment after code

The plus-equals operator += provides a convenient way to add a value to an existing variable and assign the new value back to the same variable. In the case where the variable and the value are strings, this operator performs string concatenation instead of addition. The operation is performed in-place meaning that any other variable which points to the variable being updated will also be updated.

Learn Python: Syntax
Lesson 1 of 1
  1. 1

    Python is a programming language. Like other languages, it gives us a way to communicate ideas. In the case of a programming language, these ideas are "commands" that people use to communicate with...

  2. 2

    Ironically, the first thing we're going to do is show how to tell a computer to ignore a part of a program. Text written in a program but not run by the computer is called a comment. Python inter...

  3. 3

    Now what we're going to do is teach our computer to communicate. The gift of speech is valuable: a computer can answer many questions we have about "how" or "why" or "what" it is doing. In Python, ...

  4. 4

    Computer programmers refer to blocks of text as strings. In our last exercise, we created the string "Hello world!". In Python a string is either surrounded by double quotes ( [...] ) or single q...

  5. 5

    Programming languages offer a method of storing data for reuse. If there is a greeting we want to present, a date we need to reuse, or a user ID we need to remember we can create a variable whic...

  6. 6

    Humans are prone to making mistakes. Humans are also typically in charge of creating computer programs. To compensate, programming languages attempt to understand and explain mistakes made in their...

  7. 7

    Computers can understand much more than just strings of text. Python has a few numeric data types. It has multiple ways of storing numbers. Which one you use depends on your intended purpose for ...

  8. 8

    Computers absolutely excel at performing calculations. The "compute" in their name comes from their historical association with providing answers to mathematical questions. Python performs addition...

  9. 9

    Variables that are assigned numeric values can be treated the same as the numbers themselves. Two variables can be added together, divided by [...] , and multiplied by a third variable without Pyt...

  10. 10

    Python can also perform exponentiation. In written math, you might see an exponent as a superscript number, but typing superscript numbers isn't always easy on modern keyboards. Since this operatio...

  11. 11

    Python offers a companion to the division operator called the modulo operator. The modulo operator is indicated by [...] and gives the remainder of a division calculation. If the number is divisi...

  12. 12

    The [...] operator doesn't just add two numbers, it can also "add" two strings! The process of combining two strings is called string concatenation. Performing string concatenation creates a br...

  13. 13

    Python offers a shorthand for updating variables. When you have a number saved in a variable and want to add to the current value of the variable, you can use the [...] (plus-equals) operator. ...

  14. 14

    Python strings are very flexible, but if we try to create a string that occupies multiple lines we find ourselves face-to-face with a [...] . Python offers a solution: multi-line strings. By usi...

  15. 15

    In this lesson, we accomplished a lot of things! We instructed our computers to print messages, we stored these messages as variables, and we learned to update those messages depending on the part ...

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Learn Python: Syntax

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