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python interview questions :91

How to Parsing Brackets?

  • Given a string consists of different types of brackets.
  • For example, " ([])" and "[]{}" are balanced but "([)]" and "](){" are not.You can assume these are the only characters in the string: ()[]{}.
  • If the strings are only consists of ( and ), it should not affect our solution. For example: " (())" or " (()("
  • The key to the solution is to use "stack".
def isBalanced(test):
  st = []
  for b in test:
    if b == '(':
      st.append(b)
    elif b == ')':
      if st[-1] != '(':
        return False
      else:
         st.pop()
    if b == '{':
      st.append(b)
    elif b == '}':
      if st[-1] != '{':
        return False
      else:
         st.pop()
    if b == '[':
      st.append(b)
    elif b == ']':
      if st[-1] != '[':
        return False
      else:
        st.pop()

  # openings popped off yet, return False
  if st: 
    return False

  # passed the check, return True  
  return True


if __name__ == '__main__':
  test = ['[](){}', '([)]' , '({[]})', '[()]{{}}', '[[())]]', '(({})[])', '()(()', '(()(']  
  bal = True
  for t in test:
     bal = isBalanced(t)
     print("%s is balanced? %s" %(t, bal))
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OUTPUT

[](){} is balanced? True
([)] is balanced? False
({[]}) is balanced? True
[()]{{}} is balanced? True
[[())]] is balanced? False
(({})[]) is balanced? True
()(() is balanced? False
(()( is balanced? False

python interview questions :92

How to Printing full path?

  • Print all pull paths for the files under the directory where the running python script (path.py) is.
python path

Learn python - python tutorial - python path - python examples - python programs

import os

script_location = os.path.dirname(os.path.abspath(__file__))

for dirpath, dirs, files in os.walk(script_location):
  for f in files:
    print(os.path.join(dirpath,f))
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Output:

/home/k/TEST/PYTHON/path/path.py
/home/k/TEST/PYTHON/path/d1/f1.txt
/home/k/TEST/PYTHON/path/d1/d11/f11.txt
/home/k/TEST/PYTHON/path/d1/d11/d111/f111a.txt
/home/k/TEST/PYTHON/path/d1/d11/d111/f111b.txt
/home/k/TEST/PYTHON/path/d2/f2.txt

python interview questions :93

What is the index access method called?

  • In Python [1:3] syntax on the second line .
test = (1,2,3,4,5)
print(test[1:3])
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  • The second parameter ("3") seems to be the index - 1 (3 - 1 = 2)

python interview questions :94

What is a qualified/unqualified name in Python?

  • It is the path from top-level module down to the object itself.
  • See PEP 3155, Qualified name for classes and functions.
  • If you have a nested package named foo.bar.baz with a class Spam, the method ham on that class will have a fully qualified name of foo.bar.baz.Spam.ham. ham is the unqualified name.
  • A qualified name lets you re-import the exact same object, provided it is not an object that is private to a local (function) namespace.

python interview questions :95

What is the difference between ''' and “”"?

  • Use double quotes around strings that are used for interpolation
  • single quotes for small symbol-like strings
  • Use triple double quotes for docstrings and raw string literals for regular expressions .

Example:

LIGHT_MESSAGES = {
    'English': "There are %(number_of_lights)s lights.",
    'Pirate':  "Arr! Thar be %(number_of_lights)s lights."
}

def lights_message(language, number_of_lights):
    """Return a language-appropriate string reporting the light count."""
    return LIGHT_MESSAGES[language] % locals()

def is_pirate(message):
    """Return True if the given message sounds piratical."""
    return re.search(r"(?i)(arr|avast|yohoho)!", message) is not None
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python interview questions :96

What is the difference between json.load() and json.loads() functions in Python?

  • load() loads JSON from a file or file-like object
  • loads() loads JSON from a given string or unicode object
json.load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])
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  • Deserialize fp is to a Python object using this conversion table.
json.loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])

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  • Deserialize s (a str or unicode instance containing a JSON document) to a Python object using this conversion table.

python interview questions :97

Explain Redux syntax ?

  • Create Store function from redux, takes reducer returned by combine Reducers and return a state accessible to the components defined in the Providers.
import allReducers from './YOUR_REDUCER_DIRECTORY'
var store = createStore(allReducers);

<Provider store = store>
 <YOUR_COMPONENT i.e. HEADER/>
</Provider>
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python interview questions :98

What are metaclasses? What do you use them for?

  • A metaclass is the class of a class. Like a class defines how an instance of the class behaves, a metaclass defines how a class behaves. A class is an instance of a metaclass.
  • While in Python you can use arbitrary callables for metaclasses (like Jerub shows), the more useful approach is actually to make it an actual class itself. The type is the usual metaclass in Python.
  • In case you're wondering, yes, type is itself a class, and it is its own type. You won't be able to recreate something like type purely in Python, but Python cheats a little. To create your own metaclass in Python you really just want to subclass type.
  • A metaclass is most commonly used as a class-factory. Like you create an instance of the class by calling the class, Python creates a new class (when it executes the 'class' statement) by calling the metaclass.
  • Combined with the normal __init__ and __new__ methods, metaclasses therefore allow you to do 'extra things' when creating a class, like registering the new class with some registry, or even replace the class with something else entirely.

python interview questions :99

How to do Regular expression using findall?

  • We can take only the words composed of digits from a given string using re.findall():
s = """Solar system:
Planets 8
Dwarf Planets: 5
Moons: Known = 149 | Provisional = 24 | Total = 173
Comets: More than 3400
Asteroids: More than 715000"""

import re
d = re.findall('\d+',s)
print d
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Output:

['8', '5', '149', '24', '173', '3400', '715000']

python interview questions :100

How can we copy an object in Python?

  • With new_list = old_list, we don't actually have two lists. The assignment just copies the reference to the list, not the actual list, so both new_list and old_list refer to the same list after the assignment.

Example:

>>> a = range(5)
>>> a
[0, 1, 2, 3, 4]
>>> b = a
>>> b
[0, 1, 2, 3, 4]
>>> id(a) == id(b)
True
>>> a.pop()
4
>>> b
[0, 1, 2, 3]
>>> a.remove(3)
>>> b
[0, 1, 2]
>>> del a[2]
>>> b
[0, 1]
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  • To copy the list, we can use slice:
>>> a = range(5)
>>> b = a[::]
>>> b
[0, 1, 2, 3, 4]
>>> id(a) == id(b)
False
>>> a.remove(4)
>>> b
[0, 1, 2, 3, 4]
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