Python 3 Drills for Interview Preparation
A Tour of Must-Know Python 3 Data Structures and Important Operations
Published in
9 min readJun 19, 2022
Introduction
Each part consists of a “drill” that explores important operations of a few common Python data structures.
Names of variables and methods are kept deliberately short to minimize the amount of typing required to complete the code exercises.
What This Article Is Not
This article is about learning by doing and doesn’t offer thorough explanations of the operations used. You’re left to explore these operations in more detail in your own time.
Setup
Install the latest version of Python here.
Open the Terminal, type “python3” and press Enter:
You’re now ready to start the drill — I hope you find this useful!
Basic Control Flow
a = 1
b = 2if a < b:
print('a < b')
elif a == b:
print('a = b')
else:
print('a > b') // 'a < b'while a < 3:
print(a)
a += 1
else:
print('a = 3') // '1'
// '2'
// 'a = 3'for x in [1,2]:
print(x) // 1
// 2
Numbers
5/2 // 2.5
5//2 // 2
5%2 // 1
5 ** 2 // 25
5e3 // 5000.0type(1) // <type 'int'>
type(1.1) // <type 'float'>int(1.1) // 1
float(1) // 1.0
str(1.1) // '1.1' round(1.4) // 1.0
round(1.5) // 2.0
round(1.15,1) // 1.1
round(1.16,1) // 1.2abs(-1) // 1
min(1,2) // 1
max(1,2) // 2import mathmath.floor(1.1) // 1
math.ceil(1.1) // 2
math.factorial(3) // 6(1.0).is_integer() // True
(1.1).is_integer() // False
Strings
'a b' // 'a b'
'a\'b' // "a'b"
2 * 'a' // 'aa'
'a' 'b' // 'ab'
'a' + 'b' // 'ab'x = 'abc'
len(x) // 3x.upper() // 'ABC'
x.lower() // 'abc'
x.swapcase() // 'ABC'
x.capitalize() // 'Abc'
x.islower() // True
x.isupper() // False
x.isnumeric() // False
x.isalpha() // True
x.isalnum() // Truex.count('a') // 1
x.count('A') // 0
x.startswith('a') // True
x.endswith('c') // True
x.find('b') // 1
x.find('e') // -1
x.index('b') // 1
x.index('e') // 🔥
x.find('b', 0, 1) // -1
x.index('b',0, 2) // 1x.replace('a','z') // 'zbc'
x.partition('b') // ('a', 'b', 'c')
x.partition('a') // ('', 'a', 'bc')x[0] // 'a'
x[1] // 'b'
x[2] // 'c'
x[-1] // 'c'
x[-2] // 'b'
x[-3] // 'a'
x[4] // 🔥
x[-4] // 🔥x[0:1] // 'a' (from index 0 -> 1, not including 1)
x[0:2] // 'ab'
x[0:3] // 'abc'
x[0:4] // 'abc'
x[2:3] // 'c'
x[3:4] // ''
x[2:1] // '' (2 > 1 -> '')
x[2:2] // '' (2 = 2 -> '')x[0:] // 'abc'
x[:] // 'abc'
x[1:] // 'bc' (from index position 1 onwards)
x[2:] // 'c'
x[3:] // ''
x[:1] // 'a'
x[:2] // 'ab'
x[:3] // 'abc'x[-3:] // 'abc' (max(len(x)-3,0) = 0; x[-3:] == x[0:])
x[-2:] // 'bc' (max(len(x)-2,0) = 1; x[-2:] == x[1:])
x[-1:] // 'c' (max(len(x)-1,0) = 2; x[-1:] == x[2:])
x[-4:] // 'abc' (max(len(x)-4,0) = 0; x[-4:] == x[0:])'a' + x[1:] // 'abc'
'a' + 3 * x[1:] // 'abcbcbc'[s for s in x] // ['a', 'b', 'c']
[s for s in x if s != 'b'] // ['a', 'c']s = '1=2'
a = s.split('=')
a[0] // '1'
a[1] // '2'p = ' a '
p.strip() // 'a'
p.lstrip() // 'a '
p.rstrip() // ' a's = '${p:.2f}'
s.format(p=100) // '$100.00'
Lists
x = ['a','b','a','c']x.count('a') // 2
x.count('e') // 0
x.index('a') // 0
x.index('a',1) // 2 (at index 1 or greater)
x.index('a',2) // 2 (at index 2 or greater)
x.index('a',3) // 🔥'a' in x // True
'e' in x // Falsex.reverse()
x // ['c', 'a', 'b', 'a']
x.sort()
x // ['a', 'a', 'b', 'c']
x.pop() // 'c'
x // ['a', 'a', 'b']
len(x) // 3
x.remove('a')
x // ['a', 'b']x.remove('e') // 🔥
x.append('c')
x // ['a', 'b', 'c']
x.insert(2,'a')
x // ['a', 'b', 'a', 'c'] (insert at index 2)
y = x[:]
y.pop() // 'c'
y.pop() // 'a'
x // ['a', 'b', 'a', 'c']
y // ['a', 'b']y[0] // 'a'
y[1] // 'b'
y[2] // 🔥y[-1] // 'b'
y[-2] // 'a'
y[-3] // 🔥y[:] // ['a', 'b']y[0:] // ['a', 'b']
y[1:] // ['b']
y[2:] // []
y[3:] // []y[-1:] // ['b']
y[-2:] // ['a', 'b']
y[-3:] // ['a', 'b']x[2:] = [] (x[2:] -> remove all after 2nd comma)
x // ['a', 'b']
x = []
x // []del y[1]
y // ['a']
del y[:]
y // []x + ['d','e'] // ['d', 'e']
x // []
z = x + ['d','e']
z // ['d', 'e']
z[2:] = ['f','g']
z // ['d', 'e', 'f', 'g']
z[0:1] = ['a','b']
z // ['a', 'b', 'e', 'f', 'g']
z[-2:] = []
z // ['a', 'b', 'e']
z[2] = ['e1','e2']
z // ['a', 'b', ['e1', 'e2']]
z[0] // 'a'
z[1] // 'b'
z[2][0] // 'e1'
z[2][1] // 'e2'p = [5,1,2]
max(p) // 5
min(p) // 1
sum(p) // 8
sum(p,1) // 9 (sum(p,1) -> sum(p) + 1)q = ['c','a','b']
max(q) // 'c'
min(q) // 'a'all([True,True]) // True
all([True,False]) // False
any([True,False]) // True
any([False,False]) // Falsef = ['a','b']
g = [1,2]
for f,g in zip(f,g): (think of zip fasten LHS+RHS at same levels)
print('{0}:{1}'.format(f,g)) // a:1
// b:2
More on List Comprehensions and Iteration
[0] * 3 // [0, 0, 0]
[None] * 2 // [None, None][a ** 2 for a in range(3)] // [0, 1, 4]
[a ** 2 for a in range(1,4)] // [1, 4, 9]
[(a, a ** 2) for a in range(1,4)] // [(1, 1), (2, 4), (3, 9)]
[int(x) for x in ['1','2','3']] // [1, 2, 3]list(map(int, ['1','2','3'])) // [1, 2, 3]
list(map(str.capitalize, ['aa','bb'])) // ['Aa','Bb']
list(map(pow,[1,2,3],[1,2,3])) // [1, 4, 27] (range(1,4) -> [1,2,3,4) = [1,2,3])[a for a in range(1,4)] // [1, 2, 3]
[a for a in range(1,4,1)] // [1, 2, 3]
[a for a in range(1,4,2)] // [1, 3]
[a for a in range(3,0,-1)] // [3, 2, 1]
[a for a in range(3,0,-2)] // [3, 1]
[a for a in range(3,1,-1)] // [3, 2]
[a for a in range(3,2,-1)] // [3]
[a for a in range(2,0,-1)] // [2, 1] (start 2, back 1s)
[a for a in range(1,0,-1)] // [1] (start 1, back 1s)
[a for a in range(2,0,-2)] // [2] (start 2, back 2s)[(a, b) for a in [1,2] for b in [2,3]]
// [(1, 2), (1, 3), (2, 2),(2, 3)][(a**2, b**3) for a in [1,2,3] for b in [2,3,4] if a == b]
// [(4, 8), (9, 27)]x = [5,1,2]
[a for a in x if a > 1] // [5, 2]
[a for a in x if a % 2 == 0] // [2]it = iter(x)
next(it) // 5
next(it) // 1
next(it) // 2
next(it) // 🔥it = iter(x)
while(1):
val = next(it, -1)
if val == -1:
break
else:
print(val) // 5
// 1
// 2
Stack
How to use a list like a LIFO stack.
s = ['a','b']
s // ['a','b']
s.append('c')
s // ['a', 'b', 'c']
s.pop() // 'c'
s // ['a','b']Queue
How to use a list like a FIFO queue.
from collections import dequeq = deque(['a','b'])
q // deque(['a', 'b'])
q.append('c')
q // deque(['a', 'b', 'c'])
q.popleft() // 'a'
q // deque(['b', 'c'])
list(q) // ['b', 'c']
Tuples
x = 'a','b',5
x // ('a','b', 5)
x[0] // 'a'
x[1] // 'b'
x[2] // 5x[1:] // ('b', 5)
x[1:2] // ('b',)
x[-1:] // (5,)
x[-2:] // ('b', 5)
x[-3:] // ('a', 'b', 5)
x[:] // ('a', 'b', 5)t[1] = 'c' // 🔥
del x[2] // 🔥x + (6,) // ('a', 'b', 5, 6)
x // ('a', 'b', 5)
z = x + (6,)
z // ('a', 'b', 5, 6)p = ([1,2],['d','e'])
p[0] = [3, 4] // 🔥
p[0][0] = 3
p[0][1] = 4
p // ([3, 4], ['d', 'e'])
p[1][:] = ['f','g']
p // ([3, 4], ['f', 'g'])q = (5,1,2)
len(q) // 3
min(q) // 1
max(q) // 5r = tuple([1,2])
r // (1, 2)f,g = r
f // 1
g // 2[a for a in q if a > 1] // [5, 2]([0] * 3,) * 2 // ([0, 0, 0], [0, 0, 0])t = ('a','b')
u = ','.join(t)
u // 'a,b'
Sets
x = {'a','b'}
'a' in x // True
'c' in x // Falsey = set('abccc')
y // {'a', 'c', 'b'} (no duplicates)y - x // {'c'}
x - y // set()
x | y // {'b', 'a', 'c'}
x & y // {'b', 'a'} (common elements)
x ^ y // {'c'} x[0] // 🔥x.add('c')
x // {'c', 'b', 'a'}x.discard('a')
x // {'c', 'b'}x.add('b')
x // {'c', 'b'} (no duplicates)
Dictionaries
x = {'a': 5, 'b': 10}x['a'] // 5
x['c'] // 🔥'a' in x // True
'c' in x // Falsex.keys() // dict_keys(['a', 'b'])
x.values() // dict_values([5, 10])
x.items() // dict_items[('a', 5), ('b', 10)]list(x.keys()) // ['a', 'b']
list(x.values()) // [5, 10]
list(x.items()) // [('a', 5), ('b', 10)]for a,b in x.items():
print(a,b) // 'a 5'
// 'b 10'for a,b in enumerate(x):
print(a,b) // '0, a'
// '1, b'len(x) // 2x.get('a') // 5
x.get('c') //
x.get('c',-1) // -1y = x.copy()
y['b'] = 11
x // {'a': 5, 'b': 10}
y // {'a': 5, 'b': 11}y.update({'b':15})
y // {'a': 5, 'b': 15}y.update({'c':20})
y // {'a': 5, 'b': 15, 'c': 20}y['d'] = 25
y // {'a': 5, 'b': 11, 'c': 20, 'd': 25}del y['d']
y // {'a': 5, 'b': 11, 'c': 20}y.clear()
y // {}s = ('a','b')
p = dict.fromkeys(s)
p // {'a': None, 'b': None}
p = dict.fromkeys(s,-1)
p // {'a': -1, 'b': -1}z = dict(a=5, b=10)
z // {'a': 5, 'b': 10}x == p // False
x == z // True
Some Basic Algorithms
Check if a number is prime efficiently
import mathdef is_prime(n):
for i in range(2, int(math.sqrt(n)) + 1):
if (n%i) == 0:
return False
return Trueprint(is_prime(11)) // True
print(is_prime(12)) // False
List prime numbers in a range efficiently
import mathdef primes(lower, upper):
primes = []
for num in range(lower, upper + 1):
for i in range(2, int(math.sqrt(num)) + 1):
if (num % i) == 0:
break
else:
primes.append(num)
return primesprint(primes(10,20)) // [11, 13, 17, 19]
Nth Number in Fibonacci Sequence (Recursive)
def F(n):
if n == 0: return 0
elif n == 1: return 1
else: return F(n-1) + F(n-2)F(3) // 2
Get first n Fibonacci numbers
def f(n):
nums = []
a, b = 0, 1
for i in range(n):
a, b = b, a + b
nums.append(a)
return numsprint(f(5)) // 5
Print last digit
n = 123
print(str(n)[-1]) // 3Extract digits of a number into a list
a = '123'
b = [int(i) for i in str(a)] // [1, 2, 3]Count the number of digits in a number
a = 123
count = 0while a != 0:
a //= 10
count += 1print(count) // 3
or
len(str(a)) // 3or using log (positive/negative):
import mathdef digits(n):
if n > 0:
return int(math.log10(n))+1
elif n == 0:
return 1
else:
return int(math.log10(-n))+1print(digits(-10)) // 2
print(digits(0)) // 0
print(digits(123)) // 3
Print first N natural number recursively
def p(n):
if n > 0:
p(n - 1)
print(n, end = ' ')p(3) // 1 2 3
Sum of digits in number recursively
def s(n):
if n == 0:
return 0
return n % 10 + s(n // 10)
print(s(123)) // 6Reverse string shorthand
s = 'abc'
print(s[::-1]) // 'cba'Unique divisors of a number in increasing order
import mathn = 36unique_divisors = set()
i = 1
while i < math.sqrt(n):
if n % i == 0:
unique_divisors.add(i) if n / i != i:
unique_divisors.add(int(n/i)) i += 1print(sorted(unique_divisors)) // [1, 2, 3, 4, 9, 12, 18, 36]
Greatest Common Divisor (GCD)
def gcd(x, y):
while(y):
x, y = y, x % y
return xprint(gcd(4, 6)) // 2
Lowest Common Multiple (LCM)
def lcm(x, y):
lcm = (x * y) // gcd(x,y)
return lcmprint(lcm(4, 6)) // 12
Factorial of number (iterative)
def fac(n):
result = 1
while n > 1:
result *= n
n -= 1
return resultprint(fac(3)) // 6
Factorial of a number (recursive)
def fac(n):
if n == 1:
return n
else:
return n * fac(n-1)print(fac(3)) // 6
Multiply two numbers recursively
def m(x,y):
if y == 0 :
return 0
elif y < 0:
return -(x - m(x,y+1))
else:
return x + m(x,y-1)print("3 * 2 = " , m(3,2)) // 3 * 2 = 6
print("3 * (-2) = ", m(3,-2)) // 3 * (-2) = -6
print("(-3) * 2 = ", m(-3,2)) // (-3) * 2 = -6
print("(-3) * (-2)= ", m(-3,-2)) // (-3) * (-2)= 6
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