Python Cheat Sheet Just The Basics - Arianne Colton And Sean Chen printable pdf download

ata

tructures

Python Cheat Sheet

•

tup1

= 4, 5,

Create Tuple

Note :

tup1

= (6,7,8)

• 'start' index is included, but 'stop' index is NOT.

just the basics

Create Nested Tuple

tup1

= (4,5,6), (7,8)

• start/stop can be omitted in which they default to

Convert Sequence or

the start/end.

tuple([1, 0, 2])

Iterator to Tuple

: a

reated

rianne

olton and

ean

hen

Concatenate Tuples

tup1

tup2

Application of 'step' :

Unpack Tuple

a, b,

tup1

Application of Tuple

list1[::2]

Take every other element

Reverse a string

str1[::-1]

Swap variables

eneral

calar

ypes

= a,

LIST

DICT (HASH MAP)

• Python is case sensitive

* str(), bool(), int() and float() are also explicit type

One dimensional, variable length, mutable (i.e.

• Python index starts from 0

dict1

= {'key1' : 'value1' ,

cast functions.

contents can be modified) sequence of Python objects

Create Dict

:[3, 2]}

of ANY type.

• Python uses whitespace (tabs or spaces) to indent

Create Dict from

dict(zip(keyList,

5. NoneType(None) - Python 'null' value (ONLY

code instead of using braces.

list1

= [1, 'a', 3] or

Sequence

valueList))

one instance of None object exists)

Create List

list1

= list(tup1)

Get/Set/Insert Element dict1['key1']*

HELP

• None is not a reserved keyword but rather a

list1

list2

dict1['key1'] = 'newValue'

Concatenate Lists*

unique instance of 'NoneType'

list1.extend(list2)

dict1.get('key1',

Get with Default Value

Help Home Page help()

defaultValue) **

• None is common default value for optional

Append to End of List list1.append('b')

function arguments :

Check if Key Exists

'key1' in

dict1

Function Help

help(str.replace)

Insert to Specific

list1.insert(posIdx,

'b') **

Position

Delete Element

del dict1['key1']

Module Help

help(re)

def func1(a, b,

= None)

valueAtIdx

= list1.

Get Key List

dict1.keys() ***

Inverse of Insert

pop(posIdx)

MODULE (AKA LIBRARY)

Get Value List

dict1.values() ***

• Common usage of None :

Remove First Value

list1.remove('a')

dict1.update(dict2)

Python module is simply a '.py' file

from List

Update Values

variable

is None :

# dict1 values are replaced by dict2

Check Membership

list1

=> True ***

List Module Contents

dir(module1)

Sort List

list1.sort()

6. datetime - built-in python 'datetime' module

* 'KeyError' exception if the key does not exist.

Load Module

import

module1

list1.sort(key = len)

Sort with User-

provides 'datetime', 'date', 'time' types.

Call Function from Module

module1.func1()

Supplied Function

# sort by length

'get()' by default (aka no 'defaultValue') will

• 'datetime' combines information stored in 'date'

return 'None' if the key does not exist.

and 'time'

* import statement creates a new namespace and

* List concatenation using '+' is expensive since

executes all the statements in the associated .py

*** Returns the lists of keys and values in the same

a new list must be created and objects copied

dt1

= datetime.

file within that namespace. If you want to load the

order. However, the order is not any particular

Create datetime

over. Thus,

is preferable.

strptime('20091031',

extend()

module's content into current namespace, use 'from

from String

order, aka it is most likely not sorted.

'%Y%m%d')

module1 import * '

** Insert is computationally expensive compared

Get 'date' object dt1.date()

Valid dict key types

with append.

• Keys have to be immutable like scalar types (int,

Get 'time' object dt1.time()

*** Checking that a list contains a value is lot slower

float, string) or tuples (all the objects in the tuple

Format datetime

dt1.strftime('%m/%d/%Y

than dicts and sets as Python makes a linear

calar

ypes

need to be immutable too)

to String

%H:%M')

scan where others (based on hash tables) in

constant time.

• The technical term here is 'hashability',

Change Field

dt2

= dt1.replace(minute =

Value

0, second = 30)

check whether an object is hashable with the

Check data type :

type(variable)

diff

dt1

dt2

hash('this is

string'), hash([1, 2])

Built-in 'bisect module‡

Get Difference

SIX COMMONLY USED DATA TYPES

- this would fail.

# diff is a 'datetime.timedelta' object

• Implements binary search and insertion into a

1. int/long* - Large int automatically converts to long

sorted list

SET

Note : Most objects in Python are mutable except

• 'bisect.bisect' finds the location, where 'bisect.

for 'strings' and 'tuples'

2. float* - 64 bits, there is no 'double' type

• A set is an unordered collection of UNIQUE

insort' actually inserts into that location.

elements.

3. bool* - True or False

‡ WARNING : bisect module functions do not

• You can think of them like dicts but keys only.

4. str* - ASCII valued in Python 2.x and Unicode in Python 3

check whether the list is sorted, doing so would

ata

tructures

set([3, 6, 3]) or

• String can be in single/double/triple quotes

be computationally expensive. Thus, using them

Create Set

{3, 6, 3}

• String is a sequence of characters, thus can be

in an unsorted list will succeed without error but

Test Subset

set1.issubset (set2)

may lead to incorrect results.

treated like other sequences

Note : All non-Get function call i.e.

Test Superset

set1.issuperset (set2)

list1.sort()

• Special character can be done via

or preface

examples below are in-place (without creating a new

FOR SEQUENCE TYPES †

Test sets have same

SLICING

set1

set2

with

object) operations unless noted otherwise.

content

† Sequence types include 'str', 'array', 'tuple', 'list', etc.

str1

= r'this\f?ff'

• Set operations :

TUPLE

• String formatting can be done in a number of ways

Union(aka 'or')

set1

set2

Notation list1[start:stop]

Intersection (aka 'and')

set1

set2

One dimensional, fixed-length, immutable sequence

template

= '%.2f %s

haha

$%d';

of Python objects of ANY type.

Difference

set1

set2

list1[start:stop:step]

str1

template

% (4.88, 'hola', 2)

(If step is used) §

Symmetric Difference (aka 'xor')

set1

set2

Python Cheat Sheet Just The Basics - Arianne Colton And Sean Chen

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