Guide Overview

In programming, syntax is the text that we write to create a program and semantics is the meaning or goal of that code. This guide is a starting place to help you write the syntax you need.

Each section in this guide covers a syntactical construct. Sections may include:

  • The goal of the construct
  • The syntax for using the construct
  • Examples that you can run through step by step
  • Links for further reading

How to Read Code in this Guide

  • When reading example syntax, words in ALL_CAPS represent places in the code that you fill in with custom text.
  • Lines that start with a hashtag are comments. They do not get evaluated. Comments are used to explain code.

Table of Contents

Syntax (Construct) Semantics (Goal)
1. Variables and Data Types Store data in a program.
2. Input and Output Bring data in and out of a program.
3. Conditional Statements Select what part of a program should be run.
4. For Loops Repeat actions a set number of times.
5. While Loops Repeat actions as long as condition is true.
6. Functions Group parts of a program related to a common task.
7. String Manipulation Store and retrieve information using text.

Variables and Data Types

Goal: Store data in a program.

Programmers use values to represent data and variables to keep track of values.

Here is the syntax for assigning a value to a variable:

VARIABLE = VALUE

Values can come from two places:

  • Literal values, which are defined in the code
  • Return values, which are returned by functions (see section 7)

There are four primitive types of values:

  • Integers for whole numbers such as 1, -20, and 0
  • Floats for fractional values such as 0.25 and -1.333
  • Strings for text such as 'I enjoy coding' and 'A'
  • Booleans for values that are either True or False

Here is the syntax for defining each type as a literal value:

sample_string = 'I like Tacos.'
sample_integer = 42
sample_float = 7.61
sample_boolean = True

Input and Output

Goal: Bring data in and out of a program.

Here is the syntax for taking user input:

VARIABLE = input(PROMPT)
  • Calling the input() function causes the program to display the (optional) PROMPT text (which must be a string) to the user and wait until they have entered some text.
  • When the user writes text and hits enter, the program will store the text as a string in the VARIABLE and continue by executing the next line.
  • Since the value from input will be a string, the programmer may have to convert it to another type.

Converting strings to numbers is the most common situation. Here are some examples:

number_text = input('Enter a number: ')
# number_text = '24'
number = int(number_text)
# number = 24

decimal_text = input('Enter a decimal: ')
# decimal_text = '1.76'
decimal = float(decimal_text)
# decimal = 1.76

Here is the syntax for output:

print(MESSAGE)
  • The print() function will display the MESSAGE text (which must be a string).

Conditional Statements

Goal: Select what part of a program should be run.

Here is the syntax for writing a conditional statement:

if CONDITION1:
    BRANCH_WITH_LINES_OF_CODE
elif CONDITION2:
    BRANCH_WITH_OTHER_LINES_OF_CODE
else:
    BRANCH_WITH_DIFFERENT_LINES_OF_CODE
  • A branch of a conditional statement is run if and only if the condition above it is True.
  • If no conditions are True, the else branch will run.
  • Not all branches are required. It is possible to have a statement using just if or if and some number of elif without any else branch.

A condition is any operation or value that evaluates to True or False. Here are some example conditons:

24 < 100 # True
3 + 7 == 10 # True
'cat' in 'catastrophe' # True
3 == 'dog' # False

You can read about more types of conditions here:

For Loops

Goal: Repeat actions a set number of times.

Here is the syntax for writing a for loop:

for VARIABLE_NAME in range(NUMBER):
    BODY_WITH_LINES_OF_CODE
  • The body of the loop will be repeated NUMBER times.
  • After that many runs, the program will continue by executing the next of code after the loop.

While Loops

Goal: Repeat actions as long as condition is true.

Here is the syntax for writing a while loop:

while CONDITION:
    BODY_WITH_LINES_OF_CODE
  • The body of the loop will run as long as CONDITION is True.
  • The condition will be evaluated each time, before the body is run.
  • When the loop terminates, the program will continue by executing the next of code after the loop.

Functions

Goal: Group parts of a program related to a common task.

Here is the syntax for defining a function:

def FUNCTION_NAME(PARAMETERS):
    BODY_WITH_LINES_OF_CODE
    return RETURN_VALUE
  • The function body contains all of the code to be run when the function is called.
  • The function parameters are additional data for the function.
  • Not all functions return a value. When the return statement is run, the function ends, and the program picks up execution at the next line after the function is called.
  • A function may have one return statements, several return statements, or no return statements.
  • If there are multiple return statements, only the first one to be run will take effect.

String Manipulation

Goal: Store and retrieve information using text.

Coming soon…