Python Interviews
Modulus Operator
- Check whether a number is divisible by another number using the modulus operator, %
n % k == 0
Open a file
f=open('text.txt','r')
l=f.readlines()
for i in l:
print(i.strip('\n'))
List Comprehension
[x**2 for x in range(1,11) if x % 2 == 1] [x for x in range(1,11) if x % 2 == 0]
Slicing Operator
[start : stop : steps]
Floor Division
- Floor Division operator used for dividing two operands with the result as quotient showing only digits before the decimal point:
10//5 = 2 10.0//5.0 = 2.0 10.0//4 = 2.0 10.0//7 = 1.0
List vs. Tuple
List is mutable while the Tuple is not. A tuple is allowed to be hashed. E.g: using it as a key for dictionaries.
List: a = [1,3,6] Tuple: b = (1,4,8)
Lambda vs. def
Def can hold multiple expressions while lambda is a uni-expression function. Def generates a function and designates a name to call it later. Lambda forms a function object and returns it. Def can have a return statement. Lambda can’t have return statements. Lambda supports to get used inside a list and dictionary.
Optional statements in try-except block
- Optional statements possible inside a try-except block:
“else” clause: It is useful if you want to run a piece of code when the try block doesn’t create an exception. “finally” clause: It is useful when you want to execute some steps which run, irrespective of whether there occurs an exception or not.
List Operations
Insert integer at position 5 at position 0:
a.insert(0,5)
Delete the first occurrence of integer:
a.remove(6)
Insert integer at the end of the list:
a.append(9)
Sort the list:
a.sort()
Pop the last element from the list:
a.pop()
Pop 3rd element:
list1.pop(2)
Reverse the list:
a.reverse()
Max of List(print runner-ups score):
arr = [1,4,2,6,7,6] mx = max(arr) b = [j for j in arr if j != mx] print(max(b))
List to Tuple Conv & Hashing
>>> a = [1,2,3,45,6,7] >>> a [1, 2, 3, 45, 6, 7]
>>> tuple(a) (1, 2, 3, 45, 6, 7)
>>> hash(tuple(a)) 1409902629973635913
Eval Function
You are given a polynomial of a single indeterminate (or variable), . You are also given the values of and . Your task is to verify if .
Input:
1 4 x**3 + x**2 + x + 1
a = (input()).split() x = int(a[0]) k = int(a[1]) # Sol 1: print (eval(input()) == k) # Python 2: print eval(raw_input()) == k # Sol 2: f = lambda x:eval(input()) print (f(x) == k)
Swap Case
Python has built-in string validation methods for basic data. It can check if a string is composed of alphabetical characters, alphanumeric characters, digits, etc.
str.isalnum() checks if all the characters of a string are alphanumeric (a-z, A-Z and 0-9).
>>> print 'ab123'.isalnum() True
str.isalpha() checks if all the characters of a string are alphabetical (a-z and A-Z).
>>> print 'abcD'.isalpha() True
str.isdigit() checks if all the characters of a string are digits (0-9).
>>> print '1234'.isdigit() True
str.islower() checks if all the characters of a string are lowercase characters (a-z).
>>> print 'abcd123#'.islower() True
str.isupper() checks if all the characters of a string are uppercase characters (A-Z).
>>> print 'ABCD123#'.isupper() True
def swap_case(s):
a = ""
for i in s:
if i.isupper():
a += i.lower()
elif i.islower:
a += i.upper()
else:
a += i
return a
if __name__ == '__main__':
s = input()
result = swap_case(s)
print(result)
print ''.join([i.lower() if i.isupper() else i.upper() for i in raw_input()])
def swap_case(s):
a = ""
for let in s:
if let.isupper() == True:
a+=(let.lower())
else:
a+=(let.upper())
return a
print raw_input().swapcase()
print(input().swapcase())
Arrays & Reverse it
>>> input ="1 2 3 4 -8 -10"
>>> arr = input.split(' ')
>>> arr
['1', '2', '3', '4', '-8', '-10']
>>> arr[::-1]
['-10', '-8', '4', '3', '2', '1']
Regex
Positive lookahead (?=REGEX_1)REGEX_2 (?=regex) t(?=s) matches the second t in streets. Negative lookahead (?!REGEX_1)REGEX_2 (?!regex) t(?!s) matches the first t in streets. Positive lookbehind (?<=regex) (?<=s)t matches the first t in streets. Negative lookbehind (?<!regex) (?<!s)t matches the second t in streets.