1. CS170 – Week 1
Lecture 3: Foundation
Ismail abumuhfouz

3. Semantic vs. Syntax
Syntax: The formal rules for legal statements in the language.
Semantics: The meaning of the statements - what happens when the statement is executed.
Source: Here

4. Programming Errors Syntax Semantic (Logical) Run-Time
Syntax errors are mistakes in the use of the python language, and are analogous to spelling or grammar mistakes in a language like English.
Common syntax errors include:
leaving out a keyword
Leaving out a ;
putting a keyword in the wrong place
leaving out a symbol, such as a colon, comma or brackets
misspelling a keyword
Program does not run until you fix these errors.
Logical errors are the most difficult to fix. They occur when the program runs without crashing, but produces an incorrect result.
Common logical errors include:
using the wrong variable name
getting operator precedence wrong
making a mistake in a boolean expression
off-by-one, and other numerical errors
Program run until the end, but it gives wrong results.
A problem which was not detected when the program was parsed, but is only revealed when a particular line is executed.
Common run-time errors include:
division by zero
performing an operation on incompatible types
accessing a list element, dictionary value or object attribute which doesn’t exist
trying to access a file which doesn’t exist.
Program is terminated unexpectedly while it is running. It does run all the code.
Source: Here

5. Identifiers
Identifiers are names of various program elements in the code that uniquely identify the elements. They are the names of things like variables or functions to be performed. They're specified by the programmer and should have names that indicate their purpose.

6. Identifiers Rules Are made of letters, digits and underscores.
Must begin with a letter or an underscore
Does not have a space
Can take any length.
Not a reserved word (keywords).
It is case sensitive.
Use meaningful name.

7. Keywords
keyword: An identifier that you cannot use, because it already has a reserved meaning in the python language.
Complete list of python keywords:
False
class
finally is
return
None
continue
for
lambda
try
True
def
from
nonlocal
while
and
del
global
not
with as
elif if or
yield
assert
else
import
pass
break
except in
raise

8. Strings and string literals
string: A sequence of text characters (not just letters) that can be printed or manipulated in a program.
literal: a representation of a value of a particular type
String literals in python start and end with quotation mark characters
"This is a string"

9. Comments

10. Comments Comments can be put in many standard places.
Most all programs have a "comment header" at the top of each file, naming the author and explaining what the program does.
Most programmers also place a comment at the start of every method, describing the method's behaviour.
Lastly, we can use comments inside methods to explain particular pieces of code.
Comments provide important documentation.
At this stage in our learning, it is not very useful to write comments, because we only know println statements.
More complicated programs span hundreds or thousands of lines, and it becomes very difficult to remember what each method is doing. Comments provide a simple description.
When multiple programmers work together, comments help one programmer understand the other's code.

11. Comments
If we have # anywhere on a line, everything following this on the line is a comment – ignored.
For more than a line, put your comments between
‘‘‘
Put your comments here
On multiple lines