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")
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)
Defining functions
def my_func (param1, param2):
result = param1 + param2
return result
Loops
for number in [1, 2, 3]:
print(number)
x = 0
while x < 10:
print(x)
x = x + 1
Dictionaries
numbers = {
1: "one",
2: "two"
}
print(numbers[1])
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]) |
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