©2012-2015 - Laurent Pointal Mémento v2.0.6
License Creative Commons Attribution 4 Python 3 Cheat Sheet Latest version on :
https://perso.limsi.fr/pointal/python:memento
integer, float, boolean, string, bytes Base Types ◾ ordered sequences, fast index access, repeatable values Container Types
int 783 0 -192 0b010 0o642 0xF3 list [1,5,9] ["x",11,8.9] ["mot"] []
zero binary octal hexa tuple (1,5,9) 11,"y",7.4 ("mot",) ()
float 9.23 0.0 -1.7e-6
-6 Non modifiable values (immutables) ☝ expression with only comas →tuple
bool True False ×10
""
str bytes (ordered sequences of chars / bytes)
str "One\nTwo" Multiline string: b""
escaped new line """X\tY\tZ ◾ key containers, no a priori order, fast key access, each key is unique
'I\'m' 1\t2\t3""" dictionary dict {"key":"value"} dict(a=3,b=4,k="v") {}
escaped ' escaped tab (key/value associations) {1:"one",3:"three",2:"two",3.14:"π"}
bytes b"toto\xfe\775" collection set {"key1","key2"} {1,9,3,0} set()
hexadecimal octal ☝ immutables ☝ keys=hashable values (base types, immutables…) frozenset immutable set empty
for variables, functions, Identifiers type(expression) Conversions
modules, classes… names
int("15") → 15
int("3f",16) → 63 nd
can specify integer number base in 2 parameter
a…zA…Z_ followed by a…zA…Z_0…9
◽ diacritics allowed but should be avoided int(15.56) → 15 truncate decimal part
◽ language keywords forbidden float("-11.24e8") → -1124000000.0
◽ lower/UPPER case discrimination round(15.56,1)→ 15.6 rounding to 1 decimal (0 decimal → integer number)
☺ a toto x7 y_max BigOne bool(x) False for null x, empty container x , None or False x ; True for other x
☹ 8y and for str(x)→ "…" representation string of x for display (cf. formatting on the back)
chr(64)→'@' ord('@')→64 code ↔ char
= Variables assignment
repr(x)→ "…" literal representation string of x
☝ assignment ⇔ binding of a name with a value
1) evaluation of right side expression value bytes([72,9,64]) → b'H\t@'
2) assignment in order with left side names list("abc") → ['a','b','c']
x=1.2+8+sin(y) dict([(3,"three"),(1,"one")]) → {1:'one',3:'three'}
a=b=c=0 assignment to same value set(["one","two"]) → {'one','two'}
y,z,r=9.2,-7.6,0 multiple assignments separator str and sequence of str → assembled str
a,b=b,a values swap ':'.join(['toto','12','pswd']) → 'toto:12:pswd'
a,*b=seq unpacking of sequence in str splitted on whitespaces → list of str
*a,b=seq item and list "words with spaces".split() → ['words','with','spaces']
and str splitted on separator str → list of str
x+=3 increment ⇔ x=x+3 *=
x-=2 decrement ⇔ x=x-2 /= "1,4,8,2".split(",") → ['1','4','8','2']
x=None « undefined » constant value %= sequence of one type → list of another type (via list comprehension)
del x remove name x … [int(x) for x in ('1','29','-3')] → [1,29,-3]
for lists, tuples, strings, bytes… Sequence Containers Indexing
negative index -5 -4 -3 -2 -1 Items count Individual access to items via lst[index]
positive index 0 1 2 3 4 len(lst)→5 lst[0]→10 ⇒ first one lst[1]→20
lst=[10, 20, 30, 40, 50] lst[-1]→50 ⇒ last one lst[-2]→40
positive slice 0 1 2 3 4 5 ☝ index from 0
On mutable sequences (list), remove with
negative slice -5 -4 -3 -2 -1 (here from 0 to 4)
del lst[3] and modify with assignment
lst[4]=25
Access to sub-sequences via lst[start slice:end slice:step]
lst[:-1]→[10,20,30,40] lst[::-1]→[50,40,30,20,10] lst[1:3]→[20,30] lst[:3]→[10,20,30]
lst[1:-1]→[20,30,40] lst[::-2]→[50,30,10] lst[-3:-1]→[30,40] lst[3:]→[40,50]
lst[::2]→[10,30,50] lst[:]→[10,20,30,40,50] shallow copy of sequence
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 Statements Blocks Modules/Names Imports
module truc⇔file truc.py
Comparisons : < > <= >= == != from monmod import nom1,nom2 as fct
(boolean results) ≤ ≥ = ≠ parent statement: →direct access to names, renaming with as
a and b logical and both simulta- statement block 1… import monmod →access via monmod.nom1 …
indentation !
-neously ⁝ ☝ modules and packages searched in python path (cf sys.path)
a or b logical or one or other parent statement: statement block executed only
or both Conditional Statement
statement block2… if a condition is true
☝ pitfall : and and or return value of a or ⁝ yes no yes
of b (under shortcut evaluation). if logical condition: ? ?
⇒ ensure that a and b are booleans. no
not a logical not
next statement after block 1 statements block
True Can go with several elif, elif... and only one
True and False constants ☝ configure editor to insert 4 spaces in if age<=18:
False final else. Only the block of first true
place of an indentation tab. state="Kid"
condition is executed. elif age>65:
☝ floating numbers… approximated values Maths
angles in radians ☝ with a var x: state="Retired"
if bool(x)==True: ⇔ if x: else:
Operators: + - * / // % ** from math import sin,pi… state="Active"
if bool(x)==False: ⇔ if not x:
Priority (…) × ÷ ab sin(pi/4)→0.707…
integer ÷ ÷ remainder cos(2*pi/3)→-0.4999… Exceptions on Errors
Signaling an error:
@ → matrix × python3.5+numpy sqrt(81)→9.0 √ raise ExcClass(…) error
(1+5.3)*2→12.6 log(e**2)→2.0 Errors processing: normal processing
abs(-3.2)→3.2 ceil(12.5)→13 try: raise X() errorraise
processing processing
round(3.57,1)→3.6 floor(12.5)→12 normal procesising block
pow(4,3)→64.0 modules math, statistics, random, except Exception as e: ☝ finally block for final processing
☝ usual order of operations decimal, fractions, numpy, etc. (cf. doc) error processing block in all cases.
, statements block executed as long as Conditional Loop Statement statements block executed for each Iterative Loop Statement
condition is true item of a container or iterator
☝ beware of infinite loops!
yes next
while logical condition: ? Loop Control for var in sequence: …
no finish
statements block break immediate exit statements block
continue next iteration
s = 0 initializations before the loop ☝ else block for normal Go over sequence's values
i = 1 condition with a least one variable value (here i) loop exit. s = "Some text" initializations before the loop
Algo: cnt = 0
☝ good habit : don't modify loop variable
while i <= 100: i=100 loop variable, assignment managed by for statement
s = s + i**2
i = i + 1 ☝ make condition variable change ! s= ∑ i 2 for c in s:
if c == "e": Algo: count
print("sum:",s) i=1 cnt = cnt + 1 number of e
print("found",cnt,"'e'") in the string.
print("v=",3,"cm :",x,",",y+4) Display loop on dict/set ⇔ loop on keys sequences
use slices to loop on a subset of a sequence
items to display : literal values, variables, expressions Go over sequence's index
print options: ◽ modify item at index
◽ sep=" " items separator, default space ◽ access items around index (before / after)
lst = [11,18,9,12,23,4,17]
◽ end="\n" end of print, default new line lost = []
◽ file=sys.stdout print to file, default standard output for idx in range(len(lst)): Algo: limit values greater
val = lst[idx] than 15, memorizing
s = input("Instructions:") Input
if val > 15: of lost values.
☝ input always returns a string, convert it to required type lost.append(val)
(cf. boxed Conversions on the other side). lst[idx] = 15
print("modif:",lst,"-lost:",lost)
len(c)→ items count Generic Operations on Containers Go simultaneously over sequence's index and values:
min(c) max(c) sum(c) Note: For dictionaries and sets, these for idx,val in enumerate(lst):
sorted(c)→ list sorted copy operations use keys.
val in c → boolean, membership operator in (absence not in) range([start,] end [,step]) Integer Sequences
enumerate(c)→ iterator on (index, value) ☝ start default 0, end not included in sequence, step signed, default 1
zip(c1,c2…)→ iterator on tuples containing ci items at same index
range(5)→ 0 1 2 3 4 range(2,12,3)→ 2 5 8 11
all(c)→ True if all c items evaluated to true, else False range(3,8)→ 3 4 5 6 7 range(20,5,-5)→ 20 15 10
any(c)→ True if at least one item of c evaluated true, else False range(len(seq))→ sequence of index of values in seq
Specific to ordered sequences containers (lists, tuples, strings, bytes…) ☝ range provides an immutable sequence of int constructed as needed
reversed(c)→ inversed iterator c*5→ duplicate c+c2→ concatenate
c.index(val)→ position c.count(val)→ events count function name (identifier) Function Definition
import copy named parameters
copy.copy(c)→ shallow copy of container def fct(x,y,z):
copy.deepcopy(c)→ deep copy of container fct
"""documentation"""
☝ modify original list Operations on Lists # statements block, res computation, etc.
lst.append(val) add item at end return res result value of the call, if no computed
result to return: return None
lst.extend(seq) add sequence of items at end ☝ parameters and all
lst.insert(idx,val) insert item at index variables of this block exist only in the block and during the function
lst.remove(val) remove first item with value val call (think of a “black box”)
lst.pop([idx])→value remove & return item at index idx (default last) Advanced: def fct(x,y,z,*args,a=3,b=5,**kwargs):
lst.sort() lst.reverse() sort / reverse liste in place *args variable positional arguments (→tuple), default values,
**kwargs variable named arguments (→dict)
Operations on Dictionaries Operations on Sets
d[key]=value d.clear() Operators: r = fct(3,i+2,2*i) Function Call
| → union (vertical bar char) storage/use of one argument per
d[key]→ value del d[key] & → intersection returned value parameter
d.update(d2) update/add - ^ → difference/symmetric diff. ☝ this is the use of function fct() fct
associations Advanced:
d.keys() < <= > >= → inclusion relations name with parentheses *sequence
d.values() →iterable views on Operators also exist as methods. which does the call **dict
d.items() keys/values/associations
d.pop(key[,default])→ value s.update(s2) s.copy()
s.add(key) s.remove(key) s.startswith(prefix[,start[,end]]) Operations on Strings
d.popitem()→ (key,value)
d.get(key[,default])→ value s.discard(key) s.clear() s.endswith(suffix[,start[,end]]) s.strip([chars])
d.setdefault(key[,default])→value s.pop() s.count(sub[,start[,end]]) s.partition(sep)→ (before,sep,after)
s.index(sub[,start[,end]]) s.find(sub[,start[,end]])
storing data on disk, and reading it back Files s.is…() tests on chars categories (ex. s.isalpha())
f = open("file.txt","w",encoding="utf8") s.upper() s.lower() s.title() s.swapcase()
s.casefold() s.capitalize() s.center([width,fill])
file variable name of file
opening mode encoding of s.ljust([width,fill]) s.rjust([width,fill]) s.zfill([width])
for operations ◽ 'r' read
on disk chars for text s.encode(encoding) s.split([sep]) s.join(seq)
◽ 'w' write
(+path…) files:
◽ 'a' append utf8 ascii formating directives values to format Formatting
cf. modules os, os.path and pathlib ◽ …'+' 'x' 'b' 't' latin1 …
"modele{} {} {}".format(x,y,r) str
writing ☝ read empty string if end of file reading "{selection:formatting!conversion}"
f.write("coucou") f.read([n]) → next chars
f.writelines(list of lines) if n not specified, read up to end ! ◽ Selection : "{:+2.3f}".format(45.72793)
f.readlines([n]) → list of next lines 2 →'+45.728'
Examples
f.readline() → next line nom "{1:>10s}".format(8,"toto")
☝ text mode t by default (read/write str), possible binary 0.nom →' toto'
4[key] "{x!r}".format(x="I'm")
mode b (read/write bytes). Convert from/to required type ! 0[2]
f.close() ☝ dont forget to close the file after use ! →'"I\'m"'
◽ Formatting :
f.flush() write cache f.truncate([size]) resize fill char alignment sign mini width.precision~maxwidth type
reading/writing progress sequentially in the file, modifiable with:
<>^= + - space 0 at start for filling with 0
f.tell()→position f.seek(position[,origin]) integer: b binary, c char, d decimal (default), o octal, x or X hexa…
Very common: opening with a guarded block with open(…) as f: float: e or E exponential, f or F fixed point, g or G appropriate (default),
(automatic closing) and reading loop on lines for line in f : string: s … % percent
of a text file: # processing ofline ◽ Conversion : s (readable text) or r (literal representation)
, Python Cheat Sheet
by Dave Child (DaveChild) via cheatography.com/1/cs/19/
Python sys Variables Python Class Special Methods Python String Methods (cont)
argv Command line args __new__(cls) __lt__(self, other) istitle() * title() *
builtin_module_‐ Linked C modules __init__(self, args) __le__(self, other) isupper() * translate(table)
names __del__(self) __gt__(self, other) join() upper() *
byteorder Native byte order __repr__(self) __ge__(self, other) ljust(width) zfill(width)
check_interval Signal check __str__(self) __eq__(self, other) lower() *
frequency
__cmp__(self, other) __ne__(self, other) Methods marked * are locale dependant for
exec_prefix Root directory
__index__(self) __nonzero__(self) 8-bit strings.
executable Name of executable
__hash__(self)
exitfunc Exit function name Python File Methods
__getattr__(self, name)
modules Loaded modules close() readlines(size)
__getattribute__(self, name)
path Search path flush() seek(offset)
__setattr__(self, name, attr)
platform Current platform fileno() tell()
__delattr__(self, name)
stdin, stdout, stderr File objects for I/O isatty() truncate(size)
__call__(self, args, kwargs)
version_info Python version info next() write(string)
winver Version number Python List Methods read(size) writelines(list)
append(item) pop(position) readline(size)
Python sys.argv
count(item) remove(item)
sys.argv[0] foo.py Python Indexes and Slices
extend(list) reverse()
sys.argv[1] bar len(a) 6
index(item) sort()
sys.argv[2] -c a[0] 0
insert(position, item)
sys.argv[3] qux a[5] 5
sys.argv[4] --h Python String Methods a[-1] 5
sys.argv for the command: capitalize() * lstrip() a[-2] 4
$ python foo.py bar -c qux --h center(width) partition(sep) a[1:] [1,2,3,4,5]
count(sub, start, replace(old, new) a[:5] [0,1,2,3,4]
Python os Variables
end) a[:-2] [0,1,2,3]
altsep Alternative sep
decode() rfind(sub, start ,end) a[1:3] [1,2]
curdir Current dir string
encode() rindex(sub, start, a[1:-1] [1,2,3,4]
defpath Default search path end)
b=a[:] Shallow copy of a
devnull Path of null device endswith(sub) rjust(width)
Indexes and Slices of a=[0,1,2,3,4,5]
extsep Extension separator expandtabs() rpartition(sep)
linesep Line separator find(sub, start, end) rsplit(sep) Python Datetime Methods
name Name of OS index(sub, start, rstrip() today() fromordinal(ordinal)
pardir Parent dir string end)
now(timezoneinfo) combine(date, time)
pathsep Patch separator isalnum() * split(sep)
utcnow() strptime(date, format)
sep Path separator isalpha() * splitlines()
fromtimestamp(timestamp)
Registered OS names: "posix", "nt", isdigit() * startswith(sub)
utcfromtimestamp(timestamp)
"mac", "os2", "ce", "java", "riscos" islower() * strip()
isspace() * swapcase() *
By Dave Child (DaveChild) Published 19th October, 2011. Sponsored by ApolloPad.com
cheatography.com/davechild/ Last updated 3rd November, 2020. Everyone has a novel in them. Finish
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