General Concepts

Variables

Variables may only use alphanumeric characters and _.
Variables may not start with a number.
Variables can use built-in function names but this will override the value.

Single variable assignment

a = 1
b = 's'

Multiple variable assignment

a, b = 1, 's'

Type

Returns the type of the object.

type(Object)

type('string')  # string
type(1)  # int
type(1.0)  # float

Casting

Casts the object to a datatype.

str(Object)

str(1)  # "1"
str(1.0)  # "1.0"
str(False)  # "False"

String

Things to note:

String concatentation only works with string types. You must cast objects using str(Object) to concatenate them.
Escape special characters like \n or \t using an additional back slash \.
```
"\\n"  # "\n"
```
A full string can be escaped using a literal string.
```
r'\n'  # "\n"
```

Input

Ask for user input. This value will always be a string.

input(string)

value = input("Please enter value: ")

Print

Print a text.

print(string...)

print("first", "next")  # first next

print(string..., sep=string)

print("first", "next", sep='+')  # first+next

String Format (f-strings)

Number Formats

# '.2f' ; as a two point float
f"{10:.2f}"  # 10.00

# '.2%' ; as a two point percent
f"{.10:.2%}"  # 10.00%

# '.2e' ; as a two point scientific number
f"{10:.}"  # 1.00e+01

Whitespace

# String with set width
f"{'Hello':25}"   # "Hello                    "

# Left aligned string
f"{'Hello':<25}"  # "Hello                    "

# Right aligned string
f"{'Hello':<25}"  # "                    Hello"

# Center aligned string
f"{'Hello':^25}"  # "          Hello          "

String Conditionals

Equals

# Test if strings are equal
"string" == "String"  # False

# Test if string is shorter
"str" > "string:"  # False

# Test string alphabetical order
"a" > "b"  # False

Contains

"he" in "hello"  # True

"he" not in "hello"  # False

# Get first index occurance of string or -1 if not found
"hello".find("e")  # 1

# Get number of string occurances or -1 if not found
"hello".count("l") # 2

Common Methods

# If each in string is alphanumeric
"a1".isalnum()  # True
"a 1".isalnum()  # False

# If each in string is alphabetic
"aa".isalpha()  # True

# If each in string is a digit
"1".isdigit()  # True
"2.0".isdigit()  # False

# If each in string is lowercase
"ab".islower()  # True
"Ab".isLower()  # False

# If each in string is uppercase
"AB".isupper()  # True
"Ab".isupper()  # False

# If each in string is a whitespace
" \n\t".isspace()  # True

# If string starts with
"ab".startswith("a")  # True

# If string ends with
"ab".endswith("b")  # True

Character Loop

Strings can be iterated through as a string array.

text = "abcd"
for c in text:
    print(c)
# a
# b
# c
# d

String Manipulation

Things to note:

Strings are immutable, modification will create a new string.
Strings can be instantiated using double quotes " or single quotes '.

# String repetition
"s"*5  # "sssss"

# String split
"a, b, c".split(", ")  # ["a", "b", "c"]

Substring

All values for substring are optional.

First value is the start index.
Second value is the end index (not included).
Third value is the step value.

# Return string from start to end (end index is not included)
"substring"[0:3]  # "sub"

# Returns string from start to end (relative from the right side)
"substring"[-6:]  # "string"

# Returns string from start to end (relative from the right side)
"substring"[:-6]  # "sub"

# Returns string at index
"substring"[0]  # "s"

# Returns string by step value
"0123456789"[0:10:2]  # "02468"

Common Methods

# String to lowercase
"AA".lower()  # "aa"

# String to uppercase
"aa".upper()  # "AA"

# Capitalize string
"aa".capitalize()  # "Aa"

# Remove whitespace from left
" abc<>123 ".lstrip()  # "abc<>123 "

# Remove any from list from left
" abc<>123 ".lstrip("123 abc")  # "<>123 "

# Remove whitespace from right
" abc<>123 ".rstrip()  # " abc<>123"

# Remove any from list from right
" abc<>123 ".rstrip("123 abc")  # " abc<>"

# Remove whitespace from both sides
" abc<>123 ".strip()  # "abc<>123"

# Remove any from list from both sides
" abc<>123 ".rstrip("123 abc")  # "<>"

# Replace string with another string
"hello".replace("h", "m")  # mello

Math

Things to note:

Python uses floats as the decimal type. This means you will encounter floating point precision errors.

Multiplication

10*2  # 20

# power
10**2  # 100

Division

16/5  # 3.2

# casting to int will remove decimal
int(16/5)  # 3

# divide without remainder
16//5 # 3

Common Methods

Works for both float and int.

method	description
`max(float, float)`	returns the maximum value
`min(float, float)`	returns the minimum value
`abs(float)`	returns the absolute value

Boolean

True and False

condition	description
`>`	greater than
`<`	less than
`>=`	greater than or equal to
`>=`	less than or equal to
`==`	equal to
`!=`	not equal to

Conditionals

if condition:
    print("Print if True")
elif otherCondition:
    print("Print if first False and this True")
else
    print("Print if none above")

While Loops

while condition:
  print("Execute while condition is true")

For Loops

Range

Generate an array to be used in a for-index loop.

The first optional parameter is the starting index (included). If not included it is presumed to be 0.
The second parameter is the ending index (not included).
The third optional parameter is the step value (default is 1).

range(int, int, int)

for i in range(0, 10, 2):
    print(i)
# 0, 2, 4, 6, 8

Lists

Things to note:

Lists are mutable, the values can be changed.
List values are mutable, a list contains the references to the original values.
Lists start at index 0.

Instantiate lists using []. Retrieve values using indexes.

li = ["a"]
li[0]  # "a"

Iterator

Iterate through items in a list using a for loop.

li = []
for i in li:
    print(i)

List Conditionals

li = ["a", "b"]

# If list contains
"a" in li  # True
"b" not in li  # False

List Manipulation

# Append to end of list
li = ["a"]
li += "b"  # ["a", "b"]

# Repeat in array
li = ["a"]*5  # ["a", "a", "a", "a", "a"]

# Reassign in array (only existing indexes)
li = ["a", "b"]
li[0] = "c"  # ["c", "b"] 

# Append array
li = ["a", "b"]
li += li  # ["a", "b", "a", "b"]

Common Methods

# Append to end of list
li = ["a"]
li.append("b")  # ["a", "b"]

# Insert and shift in list
li = ["a","c"]
li.insert("b", 1)  # ["a", "b", "c"]

# Remove from list (only one value)
li = ["a", "a"]
li.remove("a")  # ["a"]

# Sort list
li = [5, 4, 3, 2, 1]
li.sort()  # [1, 2, 3, 4, 5]

# Reverse list
li = [1, 2, 3, 4, 5]
li.reverse()  # [5, 4, 3, 2, 1]

Common Methods

# Retrieve from index
li = ["a"]

li[0]  # "a"
li.index(0)  # "a"

# Get minimum value
li = [2, 1]
min(li)  # 1

# Get maximum value
li = [2, 1]
max(li)  # 2

# Get length
li = ["a", "b"]
len(li)  # 2

List Duplication

Assigning a list to a variable copies the reference not value. Any changes in either list will change all the variables with the same list.

list1 = [1, 2]
list2 = list1
list2 += [3, 4]

# list1 = [1, 2, 3, 4]
# list2 = [1, 2, 3, 4]

Copying a list will create a new list with a copy of the references.

list1 = [1, 2]
list2 = list1.copy()
list2 += [3, 4]

# list1 = [1, 2]
# list2 = [1, 2, 3, 4]

list1 = [1, 2]
list3 = [list1]
list1[0] = 2  # [2, 2]

# list1 = [2, 2]
# list3 = [[2, 2]]

Tuples

Things to note:

Tuples are immutable, the references can not be changed.

tup = 1, 2, 3
tup = (1, 2, 3)

Dictionaries

Things to note:

Dictionaries can be assigned with any immutable key.

d = {'k':'v'}
d = dict(key='v')

Dictionary Conditionals

# Check if contains key
d = {'k':'v'}
'k' in d  # True
'v' not in d  # True

Dictionary Modification

# Change key value
d = {'k':1}
d['k'] = 'v'  # {"k":"v"}

# Delete key value
del d['k']  # {}

# remove and return
d = {'k':'v'}
d.pop('k')  # "v"

# remove and return or default
d = {}
d.pop('k', 'v')  # "v"
# d = {}

# remove last item*
d = {'a':1, 'b':2}
d.popitem()  # 1
# d = {'b':2}

# clear dictionary
d = {'k':'v'}
d.clear()  # {}

*before Python 3.7 this removes a random item

Common Methods

d = {'k':'v'}

# iterate through keys
for key in d.keys():
    print(key)  # "k"

# iterate through values
for val in d.values():
    print(key)  # "v"

# iterate through items
for item in d.items():
    print(key[0], key[1]) # "k v"

# get without error
d = {}
d.get('k')  # None

# get or default
d = {}
d.get('k', 'v')  # "v"

Functions

Things to note:

Functions follow the same naming conventions as variables.
Variables created in the function are only visible in the function.
Variables modified in the function are only visible in the function, they will not change global variable values.
```
v = 1

def main():
    v = 2  # outer variable is still 1

main()
```

Global variables can only be modified if the function explicetly states them as global.

v = 1

def main():
    global v
    v = 2  # sets outer v to 2

main()

Function names are defined as:

def function_name(parameters)

def function_name(parameters):
    print(parameters)
    return

Functions are called using:

function_name(parameters)

function_name("Hello")

Keyword Arguments

Things to note:

Any unnamed arguments are required.
Keyword arguments can be set in any order.
Positional arguments may not come after keyword arguments.

def function_name(required_arg, keyword_arg=1):

    return

function_name("required")
function_name("required", keyword_arg=2)

function_name(keyword_arg=2, "required")  # not allowed

Recursion

Call a method recursively. This is not recommended as it will create a new function in memory each time. A for loop is recommended instead.

def main():
    message(5)
    
def message(times):
    if times > 0:
        print("This is a recursive function.")
        message(times - 1)

main()

Libraries

Things to know:

Imports can use aliases by importing them using import as.
```
import random as rand
rand.randint(1, 10)
```

Random

random.random()

import random
random.random()  # random float between 0 and 1 (including 0 but not 1)

random.randint(start, end)

import random
random.randint(1, 10)  # random int between 1 and 10 (including start and end)

Pandas

import pandas as pd

df = pd.read_csv(r"file.csv", skiprows=1)  # read a csv file skipping header row

pd.set_option("display.max_rows", 10)  # display maximum 10 rows
pd.set_option("display.max_columns", 10)  # display maxmimum 10 columns

df.iloc[0]  # first row
df.iloc[-1]  # last row (first from end)

df.iloc[0:5, 1:2]  # rows 0-5 with columns 1:2

df.fillna(value = 0)  # fill N/A values with default

left = pd.DataFrame({"col": ["value", "value"], "col2": [1, 2]})
right = pd.DataFrame({"col": ["value", "value"], "col3": ["another", "value"]})
merge = pd.merge(left, right)  # merge on matching columns

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TOC

General Concepts

Variables

Type

Casting

String

Input

Print

String Format (f-strings)

Number Formats

Whitespace

String Conditionals

Equals

Contains

Common Methods

Character Loop

String Manipulation

Substring

Common Methods

Math

Multiplication

Division

Common Methods

Boolean

Conditionals

While Loops

For Loops

Range

Lists

Iterator

List Conditionals

List Manipulation

Common Methods

Common Methods

List Duplication

Tuples

Dictionaries

Dictionary Conditionals

Dictionary Modification

Common Methods

Functions

Keyword Arguments

Recursion

Libraries

Random

Pandas