Lesson 1: Basic Syntax

In this lesson we will learn about...

• Your First Program: "Hello, World!"
• Identifier Rules and Reserved Words
• Lines and Indentation
• Quotation
• Comments
• Input and Output

A Word of Warning about Python Versions

• Two main version of python are still in use: Python 2 and Python 3.
• We are using Python 3. Make sure you are using the correct tools!

"Hello, World!"

The "Hello, World!" program is the most basic you can run, and is traditionally your first program.

print("Hello, World!")

Hello, World!

This program simply writes Hello, World! to the screen. We'll go more in-depth about the parts of this later. Use this program to make sure your environment is set up correctly and that you can run Python code.

In IDLE:

1. You may see the python shell pop up. You can run code directly here, which is great for a few lines, but we want to be able to run a whole file of code at once. As such, even though Hello World is one line, we'll use a file.
2. Go to File > New to create a new Python file.
3. Type the code into this file, then use File > Save As... to save it with the .py file extension. Avoid spaces in file names if you can.
4. To run the code, go to Run > Run Module. The Python Shell will open and run the code in your file.

Indentation

• Blocks of code need to be indented
• The number of tabs/spaces is up to you, but must be consistent
  • Python's Style Guide suggests using 4 spaces per indent
• No braces are used, unlike many other programming languages

At this moment, you don't need to know what this code does. Rather, notice how the indentation creates blocks of code.

# Correct
if True:
    print("True")
else:
    print("False")

True

# Incorrect
if True:
print("True")
else:
print("False")

  File "<ipython-input-3-71288eeef709>", line 3
    print("True")
        ^
IndentationError: expected an indented block

Quotation

• Use single ('), double ("), or triple (''' or """) quotes to denote string literals
• Single and Double quotes span one line
  • In python, these have no syntactic difference
• Triple quotes can span multiple lines
• Use a backslash (\) to escape a quotation mark in a string
  • You do not have to escape " inside ', and vice versa

string1 = 'string'
string2 = "string"
sentence = "This is a sentence \"with double quotes\" "
sentence2 = 'This is also a sentence "with double quotes in it"'
multiline = """This is a quote 
that takes multiple lines. Notice 
how the newlines are part of the string too!"""

print(string1)
print(string2)
print(sentence)
print(sentence2)
print(multiline)

string
string
This is a sentence "with double quotes" 
This is also a sentence "with double quotes in it"
This is a quote 
that takes multiple lines. Notice 
how the newlines are part of the string too!

• Did you notice that multiline kept the line breaks when printed?
  • The new line is just a character (\n)!
  • When you use multiline strings, it gets inserted wherever you insert a new line.
  • You can also manually insert this character into any string by typing \n

Comments

Comments are pieces of text in a python file that are not interpreted as code.

Use the # to denote a comment anywhere in a line. The rest of the line after # is considered a comment. Blank lines are also ignored by python.

# This is a comment
a = 2 # This is also a comment

# blank lines also are ignored!

Input and Output

• Use input() to get input from the keyboard.
• Use print() to send output to the screen.

text = input("Enter some text: ")
print(text)

Enter some text: This is from the keyboard.
This is from the keyboard.

• The argument to input (the string between the parenthesis) is the prompt to be shown to the user.
  • Always end this with a space.