Practise qus Flashcards by Kate Doyle

Class A:
A = 1
def __init__(self):
self.a = 0

print(hasattr(A,’a’)

False

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try:
raise Exception
except:
print(‘c’)
except Exception:
print(‘b’)

Syntax Error

as except should be last branch

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try:
raise Exception(1,2,3)
except Exception as e:
print(len(e.args))

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Class A:
def __init__(self, v):
self.__a = v+1

a = A(0)
print(a.__a)

Attribute Error

__a private so have to be called like

_A__a

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class A:
def a(self):
print(‘a’)

class B:
def a(self):
print(‘b’)

class C(B,A):
def c(self):
self.a()

o = C()
o.c()

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try:
raise Exception
except BaseException:
print(‘c’)
except Exception:
print(‘b’)
except:
print(‘h’)

Base Exception is main exception

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assert var != 0

will stop the program when var == 0

as raises exception with var !=0 == False

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my_str = ‘race’

my_str = my_str.copy()

AttributeError

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my_str = ‘race’

my_str = my_str.insert(3,q)

Error

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for i in range(10):
pass

print(i)

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list1= [i for i in range(1,10)]
list2 = list1[-1:1:-1]

[9, 8, 7, 6, 5, 4, 3]

Remember the end range value is not included therefore the list reverses and stops at index = 2

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Can tuples store tuples?

yes

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Can tuples store lists?

yes

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What can you deduce from the following statement?
(Select two answers)
str = open(‘file.txt’, “rt”)

a) str is a string read in from the file named file. txt
b) a new line character translation will be performed during the reads
c) if file. txt does not exist, it will be created
d) the opened file cannot be written with the use of the str variable

b,d

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The first parameter of each method:

a) holds a reference to the currently processed object

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i = 5
while i>0:
i = i//2
if i % 2 = 0:
break
else:
i+=1
print(i)

should be:

i % 2 == 0

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i = 9
i =+ 2

What does i equal?

as i = +2
just means i equals positive 2

to add you need +=

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for i in range(1,3):
print(‘ * ‘,end=’’)
else:
print(‘ * ‘)

Star star star
* * *

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def f(n):
for i in range(1,n+1):
yield I

print(f(2))

_______________________________________
def f(n):
for i in range(1,n+1):
yield I

print([i for i in f(2)])

What is the difference in these two outputs? What do you need to remember?

__________________________

NameError as I is not defined

you need to loop through generators

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How many stars () does the snippet print?
s = ‘****’
s = s - s[2]
print(s)

Error

strings support concatenation. ‘-‘ is not supported in strings

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Which can you do to this tuple: tup = ()
a) tup[:]
b) tup.append(0)
c) tup[0]
d) del tup

a and d

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issubclass(B,B)

True

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class C():
Z = 15
def __init__(self):
self.c = 2
def multiplier(self):
self.c *= 2

y = C()
x = C()
x.multiplier()
y.multiplier()
y.multiplier()
print(x.c)

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class C():
Z = 15
def __init__(self):
self.c = 2
def multiplier():
self.c *= 2

y = C()
x = C()
x.multiplier()
y.multiplier()
y.multiplier()
print(x.c)

Type error as no self parameter in multiplier

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class A: X=0 def __init__(self): self.x = 5 class B(A): Y=1 def __init__(self): self.y = 7 a = A() b = B() Which of the following do NOT output False? A. isinstance(A,A) B. isinstance(A.X,A) C. isinstance(b,A) D. isinstance(a,A) E. isinstance(B,b)

C. isinstance(b,A) Ture D. isinstance(a,A) True E. isinstance(B,b) Error

When will isinstance() error?

When the second argument is not a class

'a'*0

len(234)

TypeError: object of type 'int' has no len()

1//2

-1//2

-1

class C(): __C=3 def __string_amplify(self,char='b',times=1): self.a += char*times c = C() c.__string_amplify('d', 2)

Error needs to be c._C__string_amplify('d', 2)

LOOK OUT FOR PRIVATE VARIABLES!!!!!! CAN ONLY CALL THEM _CLASS__VARIABLE

How do you make a class an exception?

class my_exception(Exception) my exception is now a subclass of Exception you can raise it now can make it a subclass of any Error, e.g. LookUpError

class A(): pass class B(A): pass class C(A): pass class D(C,B,A): pass D.__bases__

(__main__.C, __main__.B, __main__.A) This is a tuple and contains the classes not just the names

class A(): pass class B(A): pass class C(A): pass class D(C,B,A): pass D.__bases__[1].__bases__[0].__bases__

(object,) A is the root class, so its base is type object

class A: def __init__(self): pass a = A(1) print(hasattr(a,'A')) Output?

Error __init__ has no argument

class A: def __init__(self): pass a = A() print(hasattr(a,'A'))

False

class Ex(Exception): def __init__(self,msg): Exception.__init__(self,msg +msg) self.args = (msg,) try: raise Ex('ex') except Ex as e: print(e)

listy = [x for x in range(5)] listy = list(filter(lambda x: x-3 and x-1,listy))

[0,2,4]

hasattr(str,'__iter__')

True

What element can you not iterate through?

integers and floats

lambda x: x*2 if hasattr(x, '__iter__') else x**2, ['ku', 9, [3,8,3], (2,)]

['kuku', 81, [3,8,3,3,8,3], (2,2)]

def update_dict(): dict2 = {'R':'Best Language'} dict2.update({'Python':'Second best'}) return lambda: dict2 How do you print the dict2?

print(update_dict()()) or update_dict()()

def update_dict(): dict2 = {'R':'Best Language'} dict2.update({'Python':'Second best'}) return lambda: dict2 fun = update_dict() How do you print the dict2?

fun() or print(fun())

What does os.chdir("..") mean? os.chdir("./folder2/subfolder1") os.chdir("..") os.getcwd()

os.chdir("..") goes up one folder- folder 2 './' means parent directory '..' move to parent folder (move one level up)

f = open('file.txt', 'a+b')

We opened the file stream in binary, to be appended and updated

What is the difference between a and + ?

updating is updating/changing existing data a is just adding data 1. What do we want to do with the file? ## r - reading (DEFAULT) ## w - writing (go to byte 0) -- adding data ## a - appending (go to byte -1) -- adding data ## x - exclusive creation -- adding data 2. Do we want to change its contents? ## NO: We don't need to add anything (DEFAULT) ## YES: + (update) -- changing data 3. How do we want to read it? ## b = binary format ## t = text format (DEFAULT)

We opened the file stream in binary, to write, read or update?

'w+b'

a = [1] b=a[:] a[0]=0 b?

1 This works for LISTS

a = [1] b=a a[0]=0 b?

0 This works for LISTS

Can you do this 'python'.sort()?

NOOOOOOOOOO sort() is for lists

import sys sys.path Output?

list of strings ['/content', '/env/python', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '', '/usr/local/lib/python3.8/dist-packages', '/usr/lib/python3/dist-packages', '/usr/local/lib/python3.8/dist-packages/IPython/extensions', '/root/.ipython']

'python'.index('th')

sorted('python')

['h', 'n', 'o', 'p', 't', 'y']

uname_result(system='Linux', node='e7c812d8a0e6', release='5.10.147+', version='#1 SMP Sat Dec 10 16:00:40 UTC 2022', machine='x86_64', processor='x86_64') platform.uname() Linux-5.10.147+-x86_64-with-glibc2.27 platform.platform()

Second argument of hassatr is a ....

string

Second argument of isinstance is

class variable name (not a string)

l =[0,1,2,3] l[:3]

[0,1,2]

pair1 = ('a','b','c') pair2 = ('d','e','f') index = 0 while index < len(pair1): for item in pair2: print(pair2[index] , item) index += 1

d d d e d f e d e e e f f d f e f f

val = '2' or 1 val *= 3 print(val)

'222'

val = 1 or '2' val *= 3 print(val)

num = 12 num2 = num num = num + 1 print(num2)

12 Integer

Bytes are immutable Slicing a bytes object returns a bytes object

class A: A=1 def __init__(self): self.a = 0 print(hasattr(A,'a'))

False

'' in ' '

True

not []

True

not ''

True

not 0

True

class Class_A: def __init__(self,var): return var obj = Class_A(20) print(obj)

Error __init__ cannot return a value

i = 0 while i <4: print(i, end='-') i +=1.5 if ((i<4) == False): break else: print(0, end=' ')

0-1.5-3.0- as i is 4.5 before if statement within while loop so - is printed when i = 3 then i =4.5 and loop is broken with break

turning a dictionary into a list...

creates a list of the keys cannot change back

i = ' ' for i in ' ': print('python',end=i)

pythonpythonpythonpythonpythonpython for i in 'number of spaces'

i = ' ' while i in ' ': print('python',end=i)

pythonpythonpythonpythonpythonpython....................infinte while creates infinite loop

class A: A=1 def __init__(self): self.b = 0 class B(A): B=1 def __init__(self): self.b = 5 A.__init__(self) obj = B() obj.b

0 as A.__init__(self) is after self.b =5 the self.b = 0 in class A overrides it

li = [1,2,3,4,5,6] li[-100:]

[1,2,3,4,5,6]

int('100',2) int('0b100',2)

4 base 2 so binary 100 first argument has to be string

{2+3}*5

Error cant multiply set

(2+3,)*5

(5, 5, 5, 5, 5)

class calc: A = 20 B = 20 def __init__(self,a,b): A = a B= b print(self.A + self.B) calc(4,5)

40 as the variables in the __init__ don't do anything they are not assigned to instance or class variables

from math import * dir(math)

Name Error we have not imported math, we have imported maths contents

What does Python Standard Library contain?

Storage space for the base Python packages and types

Print(True or False)

True

Print(True and False)

False

l = [[c for c in range(r)] for r in range(3)]

[[], [0], [0, 1]]