Python Programming Reference Sheet

Basics
Print a number	print(123)
Print a string	print("test")
Adding numbers	print(1+2)
Variable assignment	number = 123
Print a variable	print(number)
Function call	x = min(1, 2)
Comment	# a comment
Types
Integer	42
String	"a string"
List	[1, 2, 3]
Tuple	(1, 2, 3)
Boolean	True
Useful functions
Write to the screen	print("hi")
Calculate length	len("test")
Minimum of numbers	min(1, 2)
Maximum of numbers	max(1, 2)
Cast to integer	int("123")
Cast to string	str(123)
Cast to boolean	bool(1)
Range of numbers	range(5, 10)
Other syntax
Return a value	return 123
Indexing	"test"[0]
Slicing	"test"[1:3]
Continue to next loop iteration	continue
Exit the loop	break
List append	numbers = numbers + [4]
List append (with method call)	numbers.append(4)
List item extraction	value = numbers[0]
List item assignment	numbers[0] = 123
Terminology
syntax	the arrangement of letters and symbols in code
program	a series of instructions for the computer
print	write text to the screen
string	a sequence of letters surrounded by quotes
variable	a storage space for values
value	examples: a string, an integer, a boolean
assignment	using = to put a value into a variable
function	a machine you put values into and values come out
call (a function)	to run the code of the function
argument	the input to a function call
parameter	the input to a function definition
return value	the value that is sent out of a function
conditional	an instruction that's only run if a condition holds
loop	a way to repeatedly run instructions
list	a type of value that holds other values
tuple	like a list, but cannot be changed
indexing	extracting one element at a certain position
slicing	extracting some elements in a row
dictionary	a mapping from keys to values
Reminders
Strings and lists are indexed starting at 0, not 1
Print and return are not the same concept
The return keyword is only valid inside functions
Strings must be surrounded by quotes
You cannot put spaces in variable or function names
You cannot add strings and integers without casting
Consistent indentation matters
Use a colon when writing conditionals, function definitions, and loops
Descriptive variable names help you understand your code better
Conditionals
if x == 1:
	print("x is one")
else:
	print("x is not one") 

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Lists
numbers = [7, 8, 9]
first_number = numbers[0]
numbers[2] = 11
if 11 in numbers:
	print("11 is in the list!")
for n in numbers:
	print(n) 

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Defining functions
def my_func (param1, param2):
	result = param1 + param2
	return result 

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Loops
for number in [1, 2, 3]:
	print(number)

x = 0
while x < 10:
	print(x)
	x = x + 1 

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Dictionaries
numbers = {
	1: "one",
	2: "two"
}

print(numbers[1]) 

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Comparisons
Equals	==
Not equals	!=
Less than	<
Less than or equal	<=
Greater than	>
Useful methods
String to lowercase	"xx".lower()
String to uppercase	"xx".upper()
Split string by spaces	"a b c".split(" ")
Remove whitespace around string	" a string ".strip()
Combine strings into one string	" ".join(["a", "b"])
String starts with	"xx".startswith("x")
String ends with	"xx".endswith("x")
List count	[1, 2].count(2)
List remove	[1, 2].remove(2)
Dictionary keys	{1: 2}.keys()
Dictionary values	{1: 2}.values()
Dictionary key/value pairs	{1: 2}.items()
Other neat bonus stuff
Zip lists	zip([1, 2], ["one", "two"])
Set	my_set = {1, 2, 3}
Set intersection	{1, 2} & {2, 3}
Set union	{1, 2} | {2, 3}
Index of list element	[1, 2, 3].index(2)
Sort a list	numbers.sort()
Reverse a list	numbers.reverse()
Sum of list	sum([1, 2, 3])
Numbering of list elements	for i, item in enumerate(items):
Read a file line by line	for line in open("file.txt"):
Read file contents	contents = open("file.txt").read()
Random number between 1 and 10	import random; x = random.randint(1, 10)
List comprehensions	[x+1 for x in numbers]
Check if any condition holds	any([True, False])
Check if all conditions hold	all([True, False])