Beyond Blocks: PythonSession #1

Beyond Blocks : Python : Session #1 by Michael Ball adapted from Glenn Sugden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

CS10 Spring 2013Thursday, April 30, 2013

Michael Ball

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Goals

• Quick introduction to Python

• Not a tutorial or “how to”

• Hope is that you’ll want to learn (more)

• Advantages over higher level languages

• Challenges of programming syntax

• It’s really like “writing BYOB on Paper”!

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Beyond Blocks: Python #1Installation: Mac Check

• Open Terminal

• Type python3 and hit return

• Type print(“hello world”) and hit return

• The result should be:

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• Get Python to "print" something with these instructions:

http://docs.python.org/faq/windows.html

(You only have to get to the "Many people use the interactive mode as a convenient yet highly programmable calculator" paragraph)

Beyond Blocks: Python #1Installation: Windows Check

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• Computer Science Circles : Run Python at Home

cemclinux1.math.uwaterloo.ca/~cscircles/wordpress/run-at-home/

Beyond Blocks: Python #1Installation: More Information

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Beyond Blocks: Python #1Installation: Version Check

Michael> python3 -VPython 3.3.4We’ll be talking about version 3.3.x here,

although version 2.7.x (which is more common) works just as well!

If curious, there’s more version info at:http://docs.python.org/whatsnew/index.html

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<demo>

Beyond Blocks: Python #1Why used “text based” programming?

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BYOB Python

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BYOB PythonVariables

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BYOB PythonVariables

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BYOB PythonVariables

NOTE:Assignment doesn’t

“evaluate” to anything, so nothing is printed!

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BYOB PythonVariables

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BYOB PythonVariables

print(var)

NOTE:Printing is one of the big differences between

Python 2 and 3. Python 3 requires () with print!For the sake of humanity, just use print()! :)

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BYOB PythonOperators

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BYOB PythonTypes

• Everything in Python has an internal “type”

• Types are determined dynamically

• x = 1

• x now has the type “int”:

• (short for “integer”)

We’ll talk about this “script” (or function) later...15

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• ‘bool’ is short for boolean

• ‘bool’s can have two values:

• True

• False

BYOB PythonTypes: bool

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• ‘bool’ is short for boolean

• ‘bool’s can have two values:

• True

• False

BYOB PythonTypes: bool

NOTE: Upper case is important!

>>> type(True)<class 'bool'>

>>> TrueTrue>>> FalseFalse

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BYOB PythonTypes: function type()

This function returns the type that Python has

assigned the identifier.

>>> type(True)<class 'bool'>>>> type(1)<class 'int'>>>> type(1.0)<class 'float'>>>> type("Hello, there!")<class 'str'>>>> type("1")<class 'str'>

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BYOB PythonOperators

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BYOB PythonOperators

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BYOB PythonOperators

• Note the double =s!

• = means assign, == means compare

• Very common source of bugs!21

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BYOB PythonOperators

= means assign,

== means compare

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BYOB PythonOperators

= means assign,

== means compare

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BYOB PythonOperators

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BYOB PythonSidebar: Division (integer vs. real/float)

Python 2 Python 3

>>> 5/60.8333333333333334>>> 5.0/6.00.8333333333333334>>> 5.0//6.00.0

>>> 5/60>>> 5.0/6.00.8333333333333334>>> 5.0//6.00.0

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BYOB PythonSidebar: Division (integer vs. real/float)

“Force” integer division

>>> 5/60.8333333333333334>>> 5.0/6.00.8333333333333334>>> 5.0//6.00.0

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BYOB PythonSidebar: Exponent

BYOB has e and 10 ,but Python can do any base & exponent!

x x

>>> 2**8256>>> 2**101024>>> 2**1001267650600228229401496703205376

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BYOB PythonConditionals

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BYOB PythonConditionals

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BYOB PythonConditionals

Notice the colon and indentation syntax!

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BYOB PythonConditionals

Notice the colon and indentation syntax!

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BYOB PythonConditionals

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BYOB PythonConditionals

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BYOB PythonLoops

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BYOB PythonLoops

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BYOB PythonLoops

Note the indentation (again)!

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BYOB PythonLoops

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BYOB PythonLoops

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BYOB PythonMore Loops

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BYOB PythonMoar [sic] Loops

There isn’t really an exact equivalent of this in Python...

We’ll talk more about this in Session #2...

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BYOB PythonFunctions: Calling

• Calling functions (the syntax) looks like this:

• Equivalent to creating & running a BYOB block:

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• Calling functions (the syntax) looks like this:

• Equivalent to creating & running a BYOB block:

BYOB PythonFunctions: Calling

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• Calling functions (the syntax) looks like this:

• Equivalent to creating & running a BYOB block:

BYOB PythonFunctions: Calling

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BYOB PythonFunctions: Calling

• Calling functions (the syntax) looks like this:

• Equivalent to creating & running a BYOB block:

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BYOB PythonFunctions : Defining

Keyword: DEF

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BYOB PythonFunctions : Defining

Name of the function

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BYOB PythonFunctions : Defining

“Arguments,” or inputs to the function

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BYOB PythonFunctions : Defining

Indentation: the key to Python and “scope.”!In Python: Indentation matters!!

We’ll talk about “scope” later...48

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BYOB PythonFunctions : Defining

pass: Python’s “placeholder”Skip this, and do nothing.

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BYOB PythonFunctions : Defining

pass: Python’s “placeholder”Skip this, and do nothing.

Functions must have a body!49

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BYOB PythonFunctions : Defining

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BYOB PythonFunctions : Defining

Hitting Return/Enter (on an empty line)“closes” (finishes) the definition.

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BYOB PythonSidebar: Keywords

• Words reserved by Python

• List at: docs.python.org/reference/lexical_analysis.html

and del from not whileas elif global or withassert else if pass yieldbreak except import class exec in raisecontinue finally is returndef for lambda try

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BYOB PythonBuilt In Functions

• http://docs.python.org/3.3/library/functions.html

abs()dict()help()min()setattr()all()dir()hex()next()slice()any()divmod()id()object()sorted()ascii()enumerate()input()

oct()staticmethod()bin()eval()int()open()str()bool()exec()isinstance()ord()sum()bytearray()filter()issubclass()pow()super()bytes()

float()iter()print()tuple()callable()format()len()property()type()chr()frozenset()list()range()vars()classmethod()getattr()locals()repr()

zip()compile()globals()map()reversed()__import__()complex()hasattr()max()round()delattr()hash()memoryview()set() 

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BYOB PythonUSEFUL: Built In Functions

• http://docs.python.org/3.3/library/functions.html

abs()help()min()max()print()range()

type()str()chr()ord()bool()float()int()

map()filter()sum()

open()

iter()len()

tuple()list()dict()set()

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BYOB PythonFunctions : Returning Values

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BYOB PythonFunctions : Returning Values

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BYOB PythonFunctions : Returning Values

“return” and “report” are equivalent!

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BYOB PythonFunctions : Recursion!

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BYOB PythonFunctions : Recursion!

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BYOB PythonFunctions : Recursion! Within Reason!

•••

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More Information

•Python.org: www.python.org

•Python Docs: www.python.org/doc/

•Python Modules: docs.python.org/modindex.html

•CodeAcademy: codeacademy.com

•Online PythonTutor: http://www.pythontutor.com

Beyond Blocks: Python #1

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More Information

•Computer Science Circles: Python

cemclinux1.math.uwaterloo.ca/~cscircles/wordpress/using-this-website/

•Dive Into Python: diveintopython.org/toc/

•Cal’s Self-Paced Center:

inst.eecs.berkeley.edu/~selfpace/class/cs9h/How to Think Like a Computer Scientist (Python Version)

www.greenteapress.com/thinkpython/thinkCSpy/html/

Beyond Blocks: Python #1

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