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Basic Python
It is an interpreted language
list(xrange()) == range() --> In python3 range is the xrange of python2 (it is not a list but a generator)
The difference between a Tuple and a List is that the position of a value in a tuple gives it a meaning but the lists are just ordered values. Tuples have structures, lists have order
To raise a number you should do: 3**2 (it isn't 3^2)
If you do 2/3 it returns 1 because you are dividing two ints. If you want decimals you should divide floats (2.0/3.0).
i >= j
i <= j
i == j
i != j
a and b
a or b
not a
float(a)
int(a)
str(d)
ord("A") = 65
chr(65) = 'A'
hex(100) = '0x64'
hex(100)[2:] = '64'
isinstance(1, int) = True
"a b".split(" ") = ['a', 'b']
" ".join(['a', 'b']) = "a b"
"abcdef".startswith("ab") = True
"abcdef".contains("abc") = True
"abc\n".strip() = "abc"
"apbc".replace("p","") = "abc"
dir(str) = List of all the availble methods
help(str) = Definition of the class str
"a".upper() = "A"
"A".lower() = "a"
"abc".capitalize() = "Abc"
sum([1,2,3]) = 6
sorted([1,43,5,3,21,4])
Join chars
3 * ’a’ = ‘aaa’
‘a’ + ‘b’ = ‘ab’
‘a’ + str(3) = ‘a3’
[1,2,3]+[4,5]=[1,2,3,4,5]
Parts of a list
‘abc’[0] = ‘a’
'abc’[-1] = ‘c’
'abc’[1:3] = ‘bc’ from [1] to [2]
"qwertyuiop"[:-1] = 'qwertyuio'
Comments
# One line comment
"""
Several lines comment
Another one
"""
Loops
if a:
#somethig
elif b:
#something
else:
#something
while(a):
#comething
for i in range(0,100):
#something from 0 to 99
for letter in "hola":
#something with letter in "hola"
t1 = (1,'2,'three')
t2 = (5,6)
t3 = t1 + t2 = (1, '2', 'three', 5, 6)
(4,) = Singelton
d = () empty tuple
d += (4,) --> Adding into a tuple
CANT! --> t1[1] == 'New value'
list(t2) = [5,6] --> From tuple to list
d = [] empty
a = [1,2,3]
b = [4,5]
a + b = [1,2,3,4,5]
b.append(6) = [4,5,6]
tuple(a) = (1,2,3) --> From list to tuple
d = {} empty
monthNumbers={1:’Jan’, 2: ‘feb’,’feb’:2}—> monthNumbers ->{1:’Jan’, 2: ‘feb’,’feb’:2}
monthNumbers[1] = ‘Jan’
monthNumbers[‘feb’] = 2
list(monthNumbers) = [1,2,’feb’]
monthNumbers.values() = [‘Jan’,’feb’,2]
keys = [k for k in monthNumbers]
a={'9':9}
monthNumbers.update(a) = {'9':9, 1:’Jan’, 2: ‘feb’,’feb’:2}
mN = monthNumbers.copy() #Independent copy
monthNumbers.get('key',0) #Check if key exists, Return value of monthNumbers["key"] or 0 if it does not exists
In the sets there are not repetitions
myset = set(['a', 'b']) = {'a', 'b'}
myset.add('c') = {'a', 'b', 'c'}
myset.add('a') = {'a', 'b', 'c'} #No repetitions
myset.update([1,2,3]) = set(['a', 1, 2, 'b', 'c', 3])
myset.discard(10) #If present, remove it, if not, nothing
myset.remove(10) #If present remove it, if not, rise exception
myset2 = set([1, 2, 3, 4])
myset.union(myset2) #Values it myset OR myset2
myset.intersection(myset2) #Values in myset AND myset2
myset.difference(myset2) #Values in myset but not in myset2
myset.symmetric_difference(myset2) #Values that are not in myset AND myset2 (not in both)
myset.pop() #Get the first element of the set and remove it
myset.intersection_update(myset2) #myset = Elements in both myset and myset2
myset.difference_update(myset2) #myset = Elements in myset but not in myset2
myset.symmetric_difference_update(myset2) #myset = Elements that are not in both
The method in __It__ will be the one used by sort in order to compare if an object of this class is bigger than other
class Person(name):
def __init__(self,name):
self.name= name
self.lastName = name.split(‘ ‘)[-1]
self.birthday = None
def __It__(self, other):
if self.lastName == other.lastName:
return self.name < other.name
return self.lastName < other.lastName #Return True if the lastname is smaller
def setBirthday(self, month, day. year):
self.birthday = date tame.date(year,month,day)
def getAge(self):
return (date time.date.today() - self.birthday).days
class MITPerson(Person):
nextIdNum = 0 # Attribute of the Class
def __init__(self, name):
Person.__init__(self,name)
self.idNum = MITPerson.nextIdNum —> Accedemos al atributo de la clase
MITPerson.nextIdNum += 1 #Attribute of the class +1
def __it__(self, other):
return self.idNum < other.idNum
Map is like: [f(x) for x in iterable] --> map(tutple,[a,b]) = [(1,2,3),(4,5)]
m = map(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, 6, 7, 8, 9]) --> [False, False, True, False, False, True, False, False, True]
zip stops when the shorter of foo or bar stops:
for f, b in zip(foo, bar):
print(f, b)
Lambda is used to define a function
(lambda x,y: x+y)(5,3) = 8 --> Use lambda as simple function
sorted(range(-5,6), key=lambda x: x** 2) = [0, -1, 1, -2, 2, -3, 3, -4, 4, -5, 5] --> Use lambda to sort a list
m = filter(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, 6, 7, 8, 9]) = [3, 6, 9] --> Use lambda to filter
reduce (lambda x,y: x*y, [1,2,3,4]) = 24
def make_adder(n):
return lambda x: x+n
plus3 = make_adder(3)
plus3(4) = 7 # 3 + 4 = 7
class Car:
crash = lambda self: print('Boom!')
my_car = Car(); my_car.crash() = 'Boom!'
mult1 = [x for x in [1, 2, 3, 4, 5, 6, 7, 8, 9] if x%3 == 0 ]
def divide(x,y):
try:
result = x/y
except ZeroDivisionError, e:
print “division by zero!” + str(e)
except TypeError:
divide(int(x),int(y))
else:
print “result i”, result
finally
print “executing finally clause in any case”
If the condition is false the string will by printed in the screen
def avg(grades, weights):
assert not len(grades) == 0, 'no grades data'
assert len(grades) == 'wrong number grades'
A generator, instead of returning something, it "yields" something. When you access it, it will "return" the first value generated, then, you can access it again and it will return the next value generated. So, all the values are not generated at the same time and a lot of memory could be saved using this instead of a list with all the values.
def myGen(n):
yield n
yield n + 1
g = myGen(6) --> 6
next(g) --> 7
next(g) --> Error
import re
re.search("\w","hola").group() = "h"
re.findall("\w","hola") = ['h', 'o', 'l', 'a']
re.findall("\w+(la)","hola caracola") = ['la', 'la']
Special meanings:
. --> Everything
\w --> [a-zA-Z0-9_]
\d --> Number
\s --> WhiteSpace char[ \n\r\t\f]
\S --> Non-whitespace char
^ --> Starts with
$ --> Ends with
- --> One or more* --> 0 or more? --> 0 or 1 occurrences
Options:
re.search(pat,str,re.IGNORECASE)
IGNORECASE
DOTALL --> Allow dot to match newline
MULTILINE --> Allow ^ and $ to match in different lines
re.findall("<.*>", "<b>foo</b>and<i>so on</i>") = ['<b>foo</b>and<i>so on</i>']
re.findall("<.*?>", "<b>foo</b>and<i>so on</i>") = ['<b>', '</b>', '<i>', '</i>']
IterTools
product
from itertools import product --> Generates combinations between 1 or more lists, perhaps repeating values, cartesian product (distributive property)
print list(product([1,2,3],[3,4])) = [(1, 3), (1, 4), (2, 3), (2, 4), (3, 3), (3, 4)]
print list(product([1,2,3],repeat = 2)) = [(1, 1), (1, 2), (1, 3), (2, 1), (2, 2), (2, 3), (3, 1), (3, 2), (3, 3)]
permutations
from itertools import permutations --> Generates combinations of all characters in every position
print list(permutations(['1','2','3'])) = [('1', '2', '3'), ('1', '3', '2'), ('2', '1', '3'),... Every posible combination
print(list(permutations('123',2))) = [('1', '2'), ('1', '3'), ('2', '1'), ('2', '3'), ('3', '1'), ('3', '2')] Every posible combination of lenght 2
combinations
from itertools import combinations --> Generates all possible combinations without repeating characters (if "ab" existing, doesn't generate "ba")
print(list(combinations('123',2))) --> [('1', '2'), ('1', '3'), ('2', '3')]
combinations_with_replacement
from itertools import combinations_with_replacement --> Generates all possible combinations from the char onwards(for example, the 3rd is mixed from the 3rd onwards but not with the 2nd o first)
print(list(combinations_with_replacement('1133',2))) = [('1', '1'), ('1', '1'), ('1', '3'), ('1', '3'), ('1', '1'), ('1', '3'), ('1', '3'), ('3', '3'), ('3', '3'), ('3', '3')]
from functools import wraps
import time
def timeme(func):
@wraps(func)
def wrapper(*args, **kwargs):
print("Let's call our decorated function")
start = time.time()
result = func(*args, **kwargs)
print('Execution time: {} seconds'.format(time.time() - start))
return result
return wrapper
@timeme
def decorated_func():
print("Decorated func!")
If you run it, you will see something like the following:
Let's call our decorated function
Decorated func!
Execution time: 4.792213439941406e-05 seconds
Last modified 2yr ago