Post on 19-Jul-2020
Python Basics!operators, expressions, computing
CS101 Lecture #2
2016-09-28
Administrivia 1/43
Administrivia
Administrivia
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Complete homework before THIS Friday at 6:00p.m.
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Warmup Quiz
Question #1
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A set of instructions executed by a computer toachieve a goal is called:A a processB a programC a procedureD an algorithm
Question #2
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A group of eight bits is called:A a nybbleB a chompC a byteD a gobble
Question #3
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Python is:A a high-level languageB a low-level language
Question #4
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Python is:A an interpreted languageB a compiled language
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Elements of Programming
What is a literal?
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Fixed value (noun)Represents data that doesn’t change(3 or 'firefly')
Executing a literal?
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Executing a literal?
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Executing a literal?
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What is an operator?
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Manipulates data (verb)
Executing an operator?
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It needs a statement to make sense!
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What is an expression?
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Combines literals and operators (phrase)
Produce a new value3 * 5100 - 23
What is an expression?
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Combines literals and operators (phrase)Produce a new value
3 * 5100 - 23
Executing an expression?
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Executing an expression?
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What is an expression?
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Can be arbitrarily complicated3 + 8*5 + 4 - 7/100
Question
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1+ 1 ∗ 2 ?=
A 4B 3C Something else
Question
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23+ 6/2− 4 ?=
A 22B 18C -9D Something else
Use parentheses!
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23+ (6/2)− 4 is always clearer.
What are some other operators?
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exponentiation, **
modulus, % (important)floor division, //
What are some other operators?
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exponentiation, **modulus, % (important)
floor division, //
What are some other operators?
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exponentiation, **modulus, % (important)floor division, //
What are some other operators?
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bitwise OR, |bitwise XOR, ˆbitwise AND, &bitwise left shift, <<bitwise right shift, >>
Example
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1 ˆ 2 ?=
A 0B 1C 2D 3
So what?
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The machine state hasn’t changed.
Programs are complex, and we need to rememberresults.
So what?
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The machine state hasn’t changed.Programs are complex, and we need to rememberresults.
How do we keep values around?
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How do we keep values around?
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How do we reuse values?
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Low-level languages refer directly to memoryaddress:ADD DATA AT 10101101 11010100TO DATA AT 11010100 01001001STORE RESULT AT 00001101 01001110
What is a variable?
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The solution: name memory locations!
Variables name a memory locationVariables store a valueThis value can change over time—it is aplaceholder.
What is a variable?
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The solution: name memory locations!Variables name a memory location
Variables store a valueThis value can change over time—it is aplaceholder.
What is a variable?
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The solution: name memory locations!Variables name a memory locationVariables store a value
This value can change over time—it is aplaceholder.
What is a variable?
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The solution: name memory locations!Variables name a memory locationVariables store a valueThis value can change over time—it is aplaceholder.
What new operator do we need?
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assignment, = (single equals sign)
How do we reuse values?
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How do we reuse values?
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How do we reuse values?
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How do we reuse values?
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How do we reuse values?
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Example
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What value is stored in the variable x?x = 17 + 7*9A 3B 31C 55D 78
Example
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What value is stored in the variable x?x = 17 + 7*9x = 3A 0B 1C 2D 3
What is a statement?
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A statement changes the state of the computer(sentence)
Example: an assignment
What is a statement?
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A statement changes the state of the computer(sentence)Example: an assignment
What is a program?
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Programs consist of series of statements:
A script is a file containing a series of Pythonstatement.A notebook (as we use in the lab) alsocollects series of Python statements.These are stored in text (there’s no magic,just text).
Each instruction is executed in order from top tobottom—together, these statements make up aprogram.
What is a program?
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Programs consist of series of statements:A script is a file containing a series of Pythonstatement.
A notebook (as we use in the lab) alsocollects series of Python statements.These are stored in text (there’s no magic,just text).
Each instruction is executed in order from top tobottom—together, these statements make up aprogram.
What is a program?
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Programs consist of series of statements:A script is a file containing a series of Pythonstatement.A notebook (as we use in the lab) alsocollects series of Python statements.
These are stored in text (there’s no magic,just text).
Each instruction is executed in order from top tobottom—together, these statements make up aprogram.
What is a program?
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Programs consist of series of statements:A script is a file containing a series of Pythonstatement.A notebook (as we use in the lab) alsocollects series of Python statements.These are stored in text (there’s no magic,just text).
Each instruction is executed in order from top tobottom—together, these statements make up aprogram.
What is a program?
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Programs consist of series of statements:A script is a file containing a series of Pythonstatement.A notebook (as we use in the lab) alsocollects series of Python statements.These are stored in text (there’s no magic,just text).
Each instruction is executed in order from top tobottom—together, these statements make up aprogram.
Our first program
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x = 10y = x ** 2y = y + y
Reminders 42/43
Reminders
Reminders
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Homework #1 due Friday, Sept. 30, 6:00 p.m.