1.0 - Table Of Contents

1.1 - What Happened?

  • .py indicates a python file

  • python interpreter is used to running the code

  • reads and parses the meaning

    • e.g. print outputs to the screen

  • syntax highlighting

    ![Coding for Planners: Up and Running with Python Planetizen Courses](/assets/planetizen-courses-python-coding-urban-design.jpg)

1.2 - Variables

  • Variables are like containers that can store information

  • add a variable message to hello_world.py

  • Edit the message and print it again

    img

1.2.1 - Naming and Usage

  • only letters (A-Z, a-z), numbers (0-9), underscore (_), but cannot start with numbers (0-9)

    ✔️: message_1

    ❌: 1_message

  • no spaces ( ), but you can separate words with an underscore (_)

    ✔️: greeting_message

    ❌: greeting message

  • don’t use keywords reserved by the language.

    ✔️: print_msg

    ❌: print

1.2.2 - Common Naming Error

  • a common mistake is misspelling a name: error.py
  • traceback is an error message
    • reason
    • location
    • possible issue

1.2.3 - Sample Code

hello_world.py

#Step 1:
message = "Hello, world!"
print(message)

#Step 2:
message = "Hello Python world!"
print(message)

error.py

message = "Hello!"
print(mesage)

Traceback (most recent call last):
  File "D:\Introduction to Python Programming\Unit 1\error.py", line 2, in <module>
    print(mesage)
NameError: name 'mesage' is not defined. Did you mean: 'message'?

1.3 - Strings

  • Everything inside of either "" or ''
    • "Hello"
    • 'World!'
  • Why do we need both?
    • 'I told my friend, "Python is the best language!"'
    • "My brother's homework is much harder than mine."

1.3.1 - Change to UPPER or lowercase

  • .title() capitalizes the first letter of all words

  • .upper() uppercase every letter

  • .lower() lowercase every letter

Example: cases.py

1.3.2 - String Concatenation

  • to concatenate is to combine two strings
  • you can use + to combine two strings

Example: concatenate.py

1.3.3 - Escape Character

  • a special character that formats the string
  • in python this character is \
  • most commonly used:
    • \n: new line
    • \t: whitespace (tab)
    • \: converts the special character after to an ordinary character
      • \\
      • \"
      • \'

Example: escape_char.py

1.3.4 - Remove Extra Spaces

  • "python" vs "python "
  • this is important when comparing strings
  • "python" is not the same as "python "
  • .rstrip() removes spaces at the end
  • .lstrip() removes spaces at the beginning
  • .strip() removes spaces at both the beginning and the end

Example: remove_space.py

1.3.5 - Common Syntax Error

  • you cannot use ' in string surround with '' and " between ""
  • Two possible solutions:
    • ' \' ' & "\" "
    • " ' " or ' " '

1.3.6 - Sample Code

cases.py

name = "john appleseed"
print(name.title())

name = "John Appleseed"
print(name.upper())
print(name.lower())

Output:

John Appleseed
JOHN APPLESEED
john appleseed

concatenate.py

first_name = "john"
last_name = "appleseed"
full_name = first_name + " " + last_name
print(full_name)
print("Hello, " + full_name.title() + "!")

Output:

john appleseed
Hello, John Appleseed!

escape_char.py

print("\tPython")
print()
print("Python\nC\nJava")
print()
print("Languages:\n\tPython\n\tC\n\tJava")

Output:

  Python

Python
C
Java

Languages:
  Python
  C
  Java

remove_space.py

best_language = " Python "
print("'" + best_language.rstrip() + "'")
print("'" + best_language.lstrip() + "'")
print("'" + best_language.strip() + "'")

Output:

' Python'
'Python '
'Python'

1.4 - Numbers

  • There are two major types of numbers
    • int, or integers. e.g. 1, 2, 3, 4
    • float, or decimals. e.g. 1.1, 2.2, 3.3, 4.4

1.4.1 - Integers

  • Can use plus (+), minus (-), multiply (*), divide (/) to do mathematical operations
  • // is used for interger division
  • ** is used to indicate a squre, a**b is the same as $a^b$
  • parenthesis can control the order of operation

Example: integer.py

1.4.2 - Floats

  • The same rules for int apply to float as well.
  • Due to the nature of the computer, addition might not be 100% accurate
    • 0.2 + 0.1 = 0.30000000000000004

Example: float.py

1.4.3 - Avoid Syntax Error With str()

  • Only elements of the same data type can be added together. e.g. str with str, numbers with numbers
  • when you try to add a str to a int or float, an TypeError occurs
  • This can be fixed with str() method to convert variables of other data type to string

1.4.4 - Sample Code

integer.py

print(2 + 3)
print(2 - 3)
print(2 * 3)
print(2 / 3)
print(2 // 3)
print(2 ** 3)
print((2 - 3) * 3)

Output:

5
-1
6
0.666
0
8
-3

float.py

print(0.1 + 0.1)
print(2 * 0.1)
print(0.2 + 0.1)
print(3 * 0.1)

Output:

0.2
0.2
0.30000000000000004
0.30000000000000004

type_error.py

age = 23
message = "Happy" + age + "rd birthday!"
print(message)

Output:

Traceback (most recent call last):
  File "tpye_error.py", line 1, in <module>
TypeError: can only concatenate str (not "int") to str

type_error_fixed.py

age = 23
message = "Happy" + str(age) + "rd birthday!"
print(message)

Output:

Happy 23rd birthday!

1.5 - Comments

1.5.1 - How to Comment

  • use `# for a inline comment
  • use ''' or """ for multi-line comment Example: comment.py

1.5.2 - Why Comment

  • purpose of code
  • how the code functions
  • inputs and outputs
  • etc.

1.4.3 - Sample Code

comment.py

#single line comment
print("Hello") #prints a greeting message

'''
multi-line comment
'''

"""
double quotation mark also works
"""

Output:

Hello

1.7 - Homework

  • check out Zen of Python by Tim Peters
  • to do so, go to command line
  • type python and press return
  • type import this and then press return again.
  • read through the lines
  • think about why these are important