Python Basics

Front 1

Help function

Back 1

help(function_name)

Front 2

Get and change working directory

Back 2

import os

os.getcwd()

os.chdir("dir_path")

Front 3

Check object class

Back 3

type(object)

Front 4

How to define a tuple

Back 4

Y=(1,"a",2,"b")

Define with parenthesis.

Once initialized, triples can't be changed.

Tuples can contain mixed object types.

Front 5

How to define a list

Back 5

X=[1,"a",2,"b"]

Define with square brackets.

Lists can be edited.

Lists can mix object types.

Front 6

How to add an object to the end of a list

Back 6

X.append("c")

Appending CHANGES the original list. It does NOT return a copy.

Lists can be appended to lists, but the entire sub-list will occupy one list element.

Front 7

How to sunset a list

Back 7

X[0:3]

Subset with square brackets

Indexing begins at 0

Second index is EXCLUSIVE, not inclusive.

Can index from end of list with negative indexes.

Front 8

Concatenate lists

Back 8

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

Front 9

Check if a value is in a list

Back 9

1 in [1,2,3,4]

Front 10

How to split a string

Back 10

S.split(" ")

Splits a string into a list of strings, separating at every space.

Front 11

How to define a dictionary

Back 11

D={"key":"value"}

Front 12

Retrieve a value from a dictionary

Back 12

Single value: D["key"]

All values: D.values()

Front 13

For loop syntax

Back 13

for i in x:

print(i)

Front 14

While loop syntax

Back 14

i=0

while(i!=len(x)):

print(x[i])

i=i+1

Front 15

If-then-else statement syntax

Back 15

if x[0]==1:

print("yes")

elif x[0]==2:

print("maybe")

else:

print("no")

Front 16

Map function

Back 16

map(func, list1, list2)

Returns a map object, which will apply func with elements from list1 and list2 as arguments. Must be queried individually. Does not return a list.

Front 17

Define a lambda

Back 17

lambda x: (x%2==0)