Python Semester 1.

1. History of Python 

: Appeared in 1991, Guido Van Rossum

: interpreted, object-oriented, high-level programming language with dynamic semantics 

 

2. Why Python?

: Attractive for Agile software development 

: use as a scripting language, powerful, applicable for GUI, games and more

: Open-source, simple and easy, shortcodes, No compilation step(fast edit-test-debug cycle, increased productivity)

: Debugging is easy (Error raises an exception)

: Huge user community 

 

3. Using python as a calculator

: Last printed expression assigned to the variable "_(underbar)."

: //(floor division-반올림결과), %(remainder), **(Powers), import math, math.sqrt(36)...etc 

: int , float, complex(use indicate the imaginary part -> 3+5j) 

: Division always turns the integer to float -> 4//2 -> 2.0

: divide with zero -> Zerodivisionerror

: Operators with mixed-type operands convert the integer operand to a floating point. 

: String is not a numeric data type(But a sequence type) 

: Adding up a string and integer variables will through an Error. 

: Float + Int -> Float 

: the actual stored value is the nearest representable binary fraction. (>>>0.1 means 0.10000.....5551115...) 

>>>print(10+0.1-10)
>>>0.09999999999999964

 

4. String 

: Single quotes(') -  all sequences will be recognised as a string

: Double quotes(") - \ shall be used along with. Some of the combinations have different functions. 

: print() function produces a more readable output (omitting enclosing quotes) 

: input() function prompts the user for input and returns the result as a string(with contents automatically escaped) 

: concatenation is the process of adding up strings

"ABC" + "de" -> ABCde / "2"+"3" -> '23' / Hi*3 -? HiHiHi / 2 * "3" ->'33' /"4" * "9" -> error/ "Hi" * 3.0 -> error 

: inside of print() function, concatenation can be achieved via + or comma

5. Type conversion 

: int(str) -> int, float(int) -> float , str(int)-> str

 

6. Variables 

: variable names can consist only of letters, numbers, and underscores(_), cannot start with a number or space

: Python is case sensitive 

: del statement to remove a variable (rarely used)

 

7. In-place operators

: allow writing arithmetic operations, such as "x=x+4 -> x+=4"