Python Interview Questions: A Review

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Python is an elegant and versatile language, used for a wide variety of applications on the Internet and in many kinds of software. Knowing this language can open many doors and career opportunities, so let’s get right to some examples of interview questions you can expect to be presented with, and some possible answers.

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Sample Python Interview Questions:

Q:  How are global and local variables defined in Python?

In general, variables that are defined outside of functions are global.  Variables defined inside a function can also be made global, by using the command ‘global x’, for example, to create a global variable called ‘x’.

Q:  Name and describe some common default modules included in Python.

• email – used to parse, handle, and generate email messages.
• string – an index of types of strings, such as all capital or lowercase letters.
• sqlite3 – used to deal with the SQLite database.
• xml – provides XML support.
• logging – creates logging classes to log system details.
• traceback – allows you to extract and print stack trace details.

Q:  Describe the difference between a list and a tuple.

A list can be changed by internal operations.  A tuple cannot be changed; it can only be operated on.  Different methods are used for each.

Q:  Write a sample program to print the complete contents of a file, with a way to catch a missing file.

try:

with open(‘filename’,’r’) as file:

print file.read()

except IOError:

print “no such file exists”

Q:  What is a negative index in Python?

While positive indices begin with position 0 and follow with 1, 2, etc., negative indices end with -1.  -2; -3 is the position before that, and so on.

Q:  Write a sample program to print the sum of all numbers from 25 to 75, inclusive.

print sum(range(25,75))

Q:  Write a sample program to print the length of each line in a particular file, not counting whitespace at the ends.

with open(“filename.txt”, “r”) as file:

print len(file.readline().rstrip())

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Q:  Write a sample program to remove the whitespace from the following string – ‘abc def geh ijk’.

s = ‘abc def geh ijk’

”.join(s.split())

Q:  Write a sample program to remove duplicate items from a given list.

This process is made easier by first sorting and scanning the list:

if List:

List.sort()

last = List[-1]

for i in range(len(List)-2, -1, -1):

if last==List[i]: del List[i]

else: last=List[i]

Q:  How would you store a list of employee first and last names?

A list of first and last names is best stored as a list of dictionaries, in the format: {‘first_name':’Example’,’last_name':’Goel’}

Q:  What is pickling and what is unpickling?

Pickling is a process by which a Python object is converted into a string representation by a pickle module.  It is then placed into a file with the dump() function.  Unpickling refers to the reverse process, in which the stored string is retrieved and turned back into an object.

Q:  Describe a few ways to generate a random number in Python.

1. random() – this command returns a floating point number, between 0 and 1.
2. uniform(x,y) – this command returns a floating point number between the values given for x and y.
3. randint(x,y) – this command returns a random integer between the values given for x and y.