Lec 4, Wed 01/15

• Tuesday 1/21 11AM: OPTIONAL review/overview session to prep for Exam 1

• Docstring vs. Comments
  • Docstring: appear once directly under the function header
  • Comments: appear anywhere in the file

• Parameters: can have no parameters or one or multiple parameters

• Return vs. Print
  • Return: caller receives the treturned value
  • Print: caller receives the None value, only the value is printed and displayed
• User Input:
  • use an input() function
• Examples

  num = input("What is your favorite number?")
  print("You entered", num) # "Echo" the input
  print("Mine", num*2)
  

  Output:
  

  What is your favorite number? 8
  You entered 8
  Mine is 88

  num = input("What is your favorite number?")
  print("You entered", num)
  my_num = 2*int(num)
  print("Mine", my_num*2)
  

  Output:
  

  What is your favorite number? 8
  You entered 8
  Mine is 16

• Strings
  • a string is a sequence of characters(letters, numbers, symbols)
  • How do we represent: She said: "Pay attention!" as a string?
    • "She said: "Pay attention!""
• Printing Strings
  • Arguments inside the print() statement, by default, are separated by spaces.
• \n : new line

• \ : something special will be done right after the backlash

• New Line

  print("Hello \n world")
  

  Output:
  

  Hello
  world

• Print Examples

  print("\"Hello, world\"")
  

  Output:
  

  “Hello, world”

  print('\"\"Hello?\" - said Mrs. O\'Brien\"')
  

  Ouput:
  

  "”Hello?” - said Mrs. O’Brien”

Announcements

• Attend optional “Ninja Hours”
• Play around with homework questions. Exam questions might be variations of homework questions.

General Questions

• Q: Do we always have 2 homeworks in one week?
  • A: Sometimes, not always. Sometimes chapters are more complicated, so there may be only one for that week.
• Q: Will we have any practice exams that will be uploaded to the class website?
  • A: I will consider this

Review…

iClicker Questions:

• Q1: Correct term for »>print(“Hello!”)?
  • Correct Answer: C) This is a function call
  • Explanation: “the »> signify that the next thing will be a function call”
• Q2: Which version of squared was used in the call?
  • Correct Answer: C) Can’t tell
  • Prof K: How could you tell which one was used?
    • Student Answer 1: set squared(8) equal to a variable and then print the variable.
      It will either output “None” or “64”
    • Student Answer 2: Use the “type” function
    • Student Answer 3: Add one to the function. If there is an error, it used the print function. If it outputs 65, it used the return function.
• Q3: Which version of squared was used in the call?
  • Correct Answer: A) Version with return
  • Explanation: If it had been version with print, an error would have occurred since
    we can’t multiply type None by 2.

New Material

User Input

• User input gets stored as a string!
• Q: is there a way to limit inputs to only numbers?
  • A: For now, we will assume they input a number and we will force it to be a number.

num = input("What is your favorite number?")
print("you said ", num)
num = int(num)        # this forces their input to be type int rather than str
print("mine is ", num + 1)

• If the user were to input a type other than just an integer, for example, a string like “eight” or a float like 8.0, there would be an error

  • ValueError: invalid literal for int() with base 10: ‘8.0’

Escape Key

>>> 'O\'Brian said "Pay attention!" '
'O\'Brian said "Pay attention!" '

The print function removes the escape characters:

>>> print('O\'Brian said "Pay attention!" ')
O'Brian said "Pay attention!"

• Note: When typing, you can use the tab key to complete a variable name