Python Review Guide.txt

SEQUENCE (String, List, Tuple)
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indexing: 				x[6]
slicing: 				x[first:last+1:step]
	slicing does not change x; it returns a new list of the sliced items.
	x='computer'
	x[1:4]				omp
	x[1:6:2]			opt
	x[3:]				puter
	x[:5]				compu
	x[-1]				r
	x[-3:]				ter
	x[:-2]				comput
adding/concatenating: 	+
multiplying: 			*
checking membership: 	in/not in. also works to check for substrings
	if value in x:
	if "dog" not in x:  
iterating:			
	for i in x:						 	# iterate items
	for i in range(0,len(x))			# iterate index
	for index, item in enumerate(x):	# iterate index & items
len(x)
min(x)
max(x)
sum(x)		  			# sum, if all numeric values
sum(x[1:3]])			# sum of items with indexes 1 and 2
sorted(x)				# does not change x. returns new sorted list
x.count(item)   		# frequency of a value or item
x.index(item)   		# returns index of first instance of item

LIST
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a = list()				# new empty list
a = [1, 2, 3]			# new list with 3 integers
a = list(tuple1)		# new list from tuple
a = [x*2 for x in range(1, 11)]		# new list with even ints 2-20
a.append(obj)			# add to end of list
a.insert(item, index)	# insert item at index
a.extend(listb)			# append listb to a
del(a[i])				# remove item at index i
item = a.pop()			# pop last item
item = a.pop(index)		# pop item at index
a.sort()				# in-place sort
a.reverse()				# reverses the order of the list
i = a.index(value)		# get index of first match
n = a.count(value)		# frequency of a value
str = "".join(a)		# joins list items into a string
len, min, max, sum, count, index	# see SEQUENCE
for loop				# see iterating a SEQUENCE
check membership		# see checking membership in a SEQUENCE

TUPLE
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items are immutable (except lists within a tuple). cannot add or delete items.
t = ()					# new empty tuple
t = tuple(list1)		# new tuple from list
t = (1, 5, 'bat')		# new tuple with 3 items
t = (22, )				# new single-item tuple
a = t[2:4]				# new list x with items 2 and 3
t = t1 + t2				# concatenate two tuples
len, min, max, sum, count, index	# see SEQUENCE
for loop				# see iterating a SEQUENCE
check membership		# see checking membership in a SEQUENCE

SET
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not sortable. not indexable. no duplicate items allowed.
s = set()				# empty set
s = {3,5,3,5}			# {5, 3}  strips duplicates
s = set(list1)			# new set from list1, strips duplicates
len(s)
if item in s:			# test membership
s.add(item)
s.remove(item)
s.pop()					# pop random item from s
s.clear()				# delete all items
s1 & s2					# AND/INTERSECT of 2 sets
s1 | s2					# OR/UNION of 2 sets
s1 ^ s2					# XOR of 2 sets

DICTIONARY
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key-value pairs. random order. not sortable. no duplicate keys.
3 ways to make a new dictionary:
	d = {'A':5, 'B':8, 'C':4}
	d = dict([('A', 5),('B', 8),('C', 4)])
	d = dict(A=5, B=8, C=4)
d['B'] = 6				# add or change item B
del d['B']				# delete item B
len(d)
if item in d:			# check membership in keys
if item in d.values:	# check membership in values
d.clear()				# delete all items
d.keys()				# returns new list of keys
d.values()				# returns new list of values
d.items()				# returns list of key-value tuple pairs in d
Iterating a dictionary:
	for key in d:
	for key,value in d.items()

QUEUE
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implement using a list.
practical for small queue only. pop will be slow for large queues.
q = list()
q.append(obj)			# push to end of queue
q.pop(0)				# pop from front of queue

STACK
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implement using a list. append adds to end of list. pop removes from end of list.
s = list()
s.append(obj)			# push to top of stack
obj = s.pop()			# pop from top of stack

INHERITANCE
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class Polygon:
	def __init__(self, id):
		self.id = id
class Rectangle(Polygon):
	def __init__(self, id, width, height):
		super().__init__(id)
		self.shape = (width, height)

STRING OPERATIONS
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len, min, max, sum, count, index	# see SEQUENCE
substrings				# see slicing a SEQUENCE
for loop				# see iterating a SEQUENCE
check membership		# see checking membership in a SEQUENCE

FILE OPERATIONS
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with open("inputFile.txt") as f1:
	for line in f1:							# iterate file, line is a string
with open("outputFile.txt", 'a') as f2:		# open in append mode
	f2.write("my data" + "\n")

ITERATOR
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i = iter(myList)
item = i.next()