Python General
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| multiply | 2*3 = 6
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| integer | Values without the decimal point
int
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| floating point | Values with decimal points and fractional parts
float
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| precedence rules | Multiplication and division before Addition and Subtraction. Parentheses explicitly specify the order in which operations should take place. Expressions are evaluated from left-to-right.
PEMDAS : Please Excuse My Dear Aunt Sally
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| exponents | 2**3 = 8
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| divide | 6/2 = 3
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| integer quotient | 14//4 = 3
the number of whole times 3 goes into 14
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| remainder | 14%3 = 2
the remainder when 14 is divided by 3
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| absolute value | abs(5) = 5
abs (-7) = 7
distance from zero on number line
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| minimum | min(18, 5) = 5
returns the lesser number
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| maximum | max (19, 5) = 19
returns the greater number
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| algebraic expressions | evaluate to a number, whether of type int or float or one of the other number types that Python supports.
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| Boolean expressions | evaluate to one of two values: True or False.
These values are said to be of Boolean type
denoted bool
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| not | Comparison operators
4 != 5
True
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| greater than | Comparison operators
5>4
True
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| less than | Comparison operators
5<6
True
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| equal to | Comparison operators
5 == (25/5)
True
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| less than or equal to | Comparison operators
4<=5
True
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| greater than or equal to | Comparison operators
5>=6
False
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| unary | applies to a single expression
EX 3 != 4
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| binary | Applies to 2 expressions
EX 3>5 or 6+7 == 13
True
EX 3>5 and 6+7 == 13
False
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| variable names | Can be lowercase, uppercase, the underscore character (_), and, except for the first character, digits 0 through 9.
1. should be meaningful, and brief
2. multiple-word name: underscore or CamelCase
3. reserved words
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| Reserved words Booleans (5) | 1. True
2. False
3. None (no value, can't decide T or F)
4. and
5. or
6. not
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| Reserved Words writing Loops (7) | 1. def (define)
2. if
3. else ( this else that)
4. elif (this, or that, or that, or...)
5. for
6. in
7. while
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| Reserved Words for seeing results or getting data (2) | 1. return
2. yield
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| Reserved Words for Variable definition and location (3) | 1. import
2. from
3. lambda
4. class
5. is (is None)
6. global
7. nonlocal
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| lambda | always 'return' statement
go anywhere a function is expected
def make_incrementor (n): return lambda x: x + n
f = make_incrementor(2)
g = make_incrementor(6)
print f(42), g(42)
44 48
http://www.secnetix.de/olli/Python/lambda_functions.hawk
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| Rerserved Words DeBugging (5) | 1. try
2. except
3. assert
4. finally
5. raise
6. with
7. as
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| Exceptions definition | when Python can't deal with script
occurs during execution
disrupts program's instructions.
must handle the exception immediately otherwise will terminate and come out.
http://www.tutorialspoint.com/python/python_exceptions.htm
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| Exception Example | try:
You do your operations here
except ExceptionI:
execute this block
except ExceptionII:
execute this block
else:
no exception, then execute this block
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| pass | does nothing
can be a place holder
It can be used when a statement is required syntactically but the program requires no action.
commonly used for creating minimal classes
null set
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| assert | assert Expression[, Arguments]
If false, AssertionError exception.
Handled like any other exception using the try-except statement, or terminates the program and produces error
http://www.tutorialspoint.com/python/assertions_in_python.htm
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| finally | place to put any code that must execute, regardless of previous errors
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| break | stops at the first value in range that fulfills statement
stops a (for) or (while) Loop, kind of control, stops the smallest tier, doesn't go into else
http://docs.python.org/release/1.5/tut/node23.html
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| Reserved Words control | 1. break
2. continue
3. pass
4. del
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| continue | go to next value in range to test
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| raise | flags error/exception to be checked later
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| class | a group of objects that have the same functions
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| with | simplifies exception handling
encapsulates common preparation
cleans up tasks in so-called context managers.
This allows common try-except-finally usage patterns to be encapsulated for convenient reuse.
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| yield | doesn't return a list, this returns an iterator So if you need the primes one at a time, in order, perhaps to call a function on each one, an iterator might be good.
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| from | Import names from a module.
like math
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| global | defined outside function, access throughout program
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| local | defined inside function body, accessed only inside declared function, not reserved
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| del | dict = {'Name': 'Zara', 'Class': 'First'};
del dict['Name']; # remove entry with key 'Name'
dict.clear(); # remove all entries in dict
del dict ; # delete entire dictionary
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