Python 3 Cheat Sheet

Base Types

• int
  783 0 -192
# binary 0b010
# octal 0o642
# hexa 0xF3
• float
  9.23 0.0 -1.7e-6
• bool
  True False
• str
  "One Two"
# New Line \n
# Escaped Tab \t
# Multiline string """X Y Z
1 2 3"""
• bytes
  b"toto\xfe\755"

Container Types

Ordered Sequences

• list
  [1,2,9] ["x",11,8.9] ["mot"]
• tuple
  non modifiable values (immutables)
  (1,5,9) 11,"y",7.4 ("mot",)
• str bytes ordered sequences of chars / bytes
  b"toto" \

Key Containers key containers, no a priori order, fast key access, each key is unique

• dictionary key value associations
  dict{"key":"value"} dict{a=3,b=4,k="v"}
• collection keys=hashable values (base types, immutables…)
  set {"key1","key2"} {1,9,3,0}

Identifiers

For variables, function, modules, classes, names, etc…
a..zA..Z_ followed by a..zA..Z_0...9

• Diacritics allowed but should be avoided
• Language keywords forbidden
• lower/UPPER case discrimination

Conversions

• int("15") → 15
• int("3f",16) → 63 can specify integer number base in 2nd parameter
• int(15.56) → 15 truncate decimal
• float("-11.24e8") → -1124000000.0
• round(15.56,1) → 15.6 rounding to 1 decimal (0 decimal → integer number)
• bool(x) False for null x, empty container x, None or False x;True for other x
• str(x) → "..." representation string of x for display
• chr(64)) → @ code <-> char
• repr(x) → "..." literal representation string of x
• bytes([72,9,64]) → b'H\t@
• list("abc") → ['a','b','c']
• dict([(3,"three"),(1,"one")]) → {1:'one',3:'three'}
• set(["one","two"]) → f{'one','two'}
• separator str and sequence of str → assembled str ':'.join(['toto','12','pswd']) → 'toto:12:pswd'
• str splitted on whitespaces → list of str "words with spaces".split() → ['words','with','spaces']
• str splitted on separator str → list of str "1,4,8,2".split(",") → ['1','4','8','2']
• sequence of one type → list of another type (via list comprehension) [int(x) for x in ('1','29','-3')] → [1,29,-3]

Variables Assignment

assignment ⇔ binding of a name with a value

1. evaluation of right side expression value
2. assignment in order with left side names

• x=1.2+8+sin(y)
• a=b=c=0 assignment to same value
• y, z, r=9.2,-7.6,0 multiple assignments
• a, b=b, a values swap
• a, *b=seq
• *a, b=seq unpacking of sequences in item and list
• x=None « undefined » constant value
• del x remove name x
• x+=3 increment ⇔ x=x+3
• x-=2 decrease ⇔ x=x-3

  Operator	Example	Same As
  +=	x+=3	x=x+3
  -=	x-=2	x=x-2
  *=	x*=3	x=x*3
  /=	x/=3	x=x/3
  %=	x%=3	x=x%3

Sequence Containers Indexing

lst = [10, 20, 30, 40, 50]
Length Count: len(lst)→5 index from 0 (here from 0 to 4)
Individual access to items via lst[index]

• lst[0]→10 first item
• lst[-1]→50 last item
• lst[1]→20 second item
• lst[-2]→40 second to last item

Access to sub-sequences via lst [start slice: end slice: step]

• lst[:-1]→[10,20,30,40]
• lst[1:-1]→[20,30,40]
• lst[::2]→[10,30,50]
• lst[::-1]→[50,40,30,20,10]
• lst[::-2]→[50,30,10]
• lst[:]→[10,20,30,40,50] shallow copy of sequence
• lst[1:3]→[20,30]
• lst[-3:-1]→[30,40]
• lst[:3]→[10,20,30]
• lst[3:]→[40,50]
  Missing slice indication → from start / up to end.
  On mutable sequences (list), remove with del lst[3:5] and modify with assignment lst[1:4]=[15,25]

Boolean Logic

Modules/Names Imports

• from monmod import nom1,nom2 as fct renaming with as
• import monmod access via monmod.nom1

Conditional Statements

if logical condition:
    statemnet block

• Can go with several elif, elif… and only one final else. Only the block of first true condition is executed.

if age<=18:
    state="Kid"
elif age>65:
    state="Retired"
else:
    state="Active"

Conditional Loop Statement

statement block executed as long as condition is true

while logical condition: 
    statement block

Loop Control

• break immediate exit
• continue next iteration
• else normal loop exit

Iterative Loop Statement

statement block executed for each item of a container or iterator

for var in sequence: 
    statement block

lst = [11,18,9,12,23,4,17]
lost = []
for idx in range(len(lst)):
    val = lst[idx]
    if val > 15:
        lost.append(val)
        lst[idx] = 15
print("modif:",lst,"-lost:",lost)

Math

from math import sin, pi, cos, sqrt, log, ceil, floor

Container Options

• len(c) items count
• min(c) max(c) sum(c)
• sorted(c) list sorted copy
• val in c boolean, membership operator in (absence not in)
• enumerate(c) iterator on (index, value)
• zip(c1,c2) iterator on tuples containing c, items at same index
• all(c) True if all c items evaluated to true, else False
• any(c) True if at least one item of c evaluated to true, else False Specific to ordered sequence containers (list, typles, strings, bytes)
• reversed(c) inversed iterator
• c.index(val)
• c.count(val) import copy
• copy.copy(c) shallow copy of container
• copy.deepcopy(c) deep copy of container

Operations on Lists

• lst.append(val)
• lst.extend(seq) add sequence of items at end
• lst.insert(idx,val)
• lst.remove(val)
• lst.pop(idx) remove and return item at index (default last)
• lst.sort()
• lst.reverse()

References

Python Cheat Sheet