1. General Computer Science for Engineers CISC 106 Lecture 03
Dr. John Cavazos
Computer and Information Sciences
09/07/2010

2. Machine Language to Assembly
Computers only understand machine language
Machine language is difficult to write
Assembly language uses short words that are known as mnemonics
Assembler is used to translate an assembly language program to machine language
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3. Do you know of any other high-level computer programming languages?
High-Level Languages
Assembly language is referred to as a low-level language
High-level languages allow you to create powerful and complex programs without knowing how the CPU works, using words that are easy to understand.
For example:
Ada, BASIC, Python, C++, Ruby, Visual Basic
Do you know of any other high-level computer programming languages?
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4. Compilers and Interpreters
The statements written in a high-level language are called source code or simply code
Source code is translated to machine language using a compiler or an interpreter
Syntax error is a mistake that the compiler / interpreter can catch:
Misspelled word
Missing punctuation character
Incorrect use of an operator
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5. Compilers
Compiler is a program that translates a high-level language program into a separate machine language program
Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

6. Interpreter
An interpreter is a program that both translates and executes the instructions in a high-level language program
Python language uses an interpreter
Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

7. Python Introduction Python programs can be saved in files
Python interpreter :
Can run programs
Can execute individual statements typed at prompt
IDLE is a development environment
Can be used to write, execute, and test Python programs
Copyright © 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

8. Python Interpreter
A program that can read Python programming statements and execute them is the Python interpreter
Python interpreter has two modes:
Interactive mode waits for a statement from the keyboard and executes it
Script mode reads the contents of a file (Python program or Python script) and interprets each statement in the file
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9. Python Interpreter (cont’d)
Interpreter Mode
Invoke Python interpreter
>>> is prompt indicating interpreter is waiting for a Python statement
>>> print ‘Python programming is fun!’
Python programming is fun!
>>>
Statements typed in interactive mode are not saved as a program
[ENTER]
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10. Python Interpreter (cont’d)
Script Mode
Use a text editor to create a file containing the Python statements
Save the file with a .py extension
Run the program:
> python test.py
[ENTER]
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11. What is a function?
inputs
output

12. Designing Programs Use Design Recipes 5 Steps
TAs will make sure you follow steps!

13. Design Recipe : Step 1 : Docstring
Read the problem.
Inputs : What kinds of data does the function consume?
Output : What kind of data does it produce?
Write a short purpose statement. List all required input parameters (use meaningful names). Provide data kinds for each parameter, including the return value.

14. Design Recipe : Step 1 (example)
Write a function that computes the area of a rectangle, given the width and height.

15. Design Recipe : Step 2 : Function Header
Write the function header, using the information from the contract.
def area(width, height):
inputs
keyword
function name

16. Design Recipe : Step 3 : Testing
Make up examples of inputs. What should your program produce for those inputs? Write these as unit tests using assertEqual.
assertEqual(area(0,0), 0)
assertEqual(area(10,10), 100)

17. Design Recipe : Step 4 : Function Body
Now write your function body. Look closely at your examples, and try to see the pattern. How can the inputs be turned into the desired outputs?
def area(width, height): …
return width * height

18. Design Recipe : Step 5 : Put it all Together!
Now put it all together into one Python file,

19. Extra Slides

20. Atomic Data - Numbers : floats, integers
Can use “type” to find out the data type of something.
type(5) # int
type (5.0) # float
Strings Some examples : “hello” and ‘hello’
type(“hello”) # str
“hello” + “world” # plus symbol concatenates two strings

21. Atomic Data (cont’d) Booleans True False True and False True or False
type(True) # bool

22. Atomic Data (cont’d) # Can mix and match numbers >>> 3 + 5.0
8.0
# Cannot mix numbers and strings
“hello” + 3
# Builtin convert between types
str(100)
int(“5”)

23. Programming, Computing, Functions
Programming = writing “arithmetic” expressions
Computing = finding the value of an expression
Functions = programs that take inputs and compute outputs

24. Simple Function
What is the expression being computed? X= 1 2 3 4 5 Y= 9 16 ??

25. Simple Function
The python function to compute this table.
def compute_square(x) :
"""
returns the square of the input value x that is passed in
x -- int
return – int
return x * x X= 1 2 3 4 5 Y= 9 16 ??