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Python Interview Questions & Answers - Learning Mode
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Python Interview Questions & Answers - Learning Mode

Python is a widely used high-level, general-purpose, interpreted, dynamic programming language. Its design philosophy emphasizes code readability, and its syntax allows programmers to express concepts in fewer lines of code than possible in languages such as C++ or Java. Developer‎: ‎Python Software Foundation. Python is an interpreted, object-oriented programming language similar to PERL, that has gained popularity because of its clear syntax and readability. Python is said to be relatively easy to learn and portable, meaning its statements can be interpreted in a number of operating system.

Try Python Interview Questions & Answers - Exam Mode

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Python Interview Questions & Answers - Learning Mode
Try Python Interview Questions & Answers - Exam Mode
Question: How do I avoid blocking in the connect() method of a socket?

Answer: The select module is commonly used to help with asynchronous I/O on sockets. Source: CoolInterview.com
Question: How do you make a higher order function in Python?

Answer: You have two choices: you can use nested scopes or you can use callable objects. For example, suppose you wanted to define linear(a,b) which returns a function f(x) that computes the value a*x+b. Using nested scopes:

def linear(a,b):
def result(x):
return a*x + b
return result

Or using a callable object:

class linear:
def __init__(self, a, b):
self.a, self.b = a,b
def __call__(self, x):
return self.a * x + self.b

In both cases:

taxes = line Source: CoolInterview.com
Question: Where is the math.py (socket.py, regex.py, etc.) source file?

Answer: There are (at least) three kinds of modules in Python:

1. modules written in Python (.py);
2. modules written in C and dynamically loaded (.dll, .pyd, .so, .sl, etc);
3. modules written in C and linked with the interpreter; to get a list of these, type:
import sys
print sys.builtin_module_names Source: CoolInterview.com
Question: How do I submit bug reports and patches for Python?

Answer: To report a bug or submit a patch, please use the Roundup installation at http://bugs.python.org/.

You must have a Roundup account to report bugs; this makes it possible for us to contact you if we have follow-up questions. It will also enable Roundup to send you updates as we act on your bug. If you had previously used SourceForge to report bugs to Python, you can obtain your Roundup password through Roundup's password reset procedure. Source: CoolInterview.com
Question: Explain about raising error exceptions

Answer: In python programmer can raise exceptions using the raise statement. When you are using exception statement you should also specify about error and exception object. This error should be related to the derived class of the Error. We can use this to specify about the length of the user name, password field, etc. Source: CoolInterview.com
Question: How do I convert a number to a string?

Answer: To convert, e.g., the number 144 to the string '144', use the built-in function str(). If you want a hexadecimal or octal representation, use the built-in functions hex() or oct(). For fancy formatting, use the % operator on strings, e.g. "%04d" % 144 yields '0144' and "%.3f" % (1/3.0) yields '0.333'. See the library reference manual for details. Source: CoolInterview.com
Question: What is Python good for?

Answer: Python is a high-level general-purpose programming language that can be applied to many different classes of problems.

The language comes with a large standard library that covers areas such as string processing (regular expressions, Unicode, calculating differences between files), Internet protocols (HTTP, FTP, SMTP, XML-RPC, POP, IMAP, CGI programming), software engineering (unit testing, logging, profiling, parsing Python code), and operating system interfaces (system calls, filesystem Source: CoolInterview.com
Question: How do I modify a string in place?

Answer: You can't, because strings are immutable. If you need an object with this ability, try converting the string to a list or use the array module:

>>> s = "Hello, world"
>>> a = list(s)
>>>print a
['H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd']
>>> a[7:] = list("there!")
>>>''.join(a)
'Hello, there!'
CoolInterview.com
Question: How do I call an object's method from C?

Answer: The PyObject_CallMethod() function can be used to call an arbitrary method of an object. The parameters are the object, the name of the method to call, a format string like that used with Py_BuildValue(), and the argument values:

PyObject *
PyObject_CallMethod(PyObject *object, char *method_name,
char *arg_format, ...);

This works for any object that has methods -- whether built-in or user-defined. You are responsible for eventually Py_DECREF'ing the return value.

Source: CoolInterview.com
Question: How to Debugging in python?

Answer: Syntax and header errors are hard to catch unless you have access to the server logs. Syntax error messages can be seen if the script is run in a local shell before uploading to the server.

For a nice exceptions report there is the cgitb module. It will show a traceback inside a context. The default output is sent to standard output as HTML:

#!/usr/bin/env python
print "Content-Type: text/html"
print
import cgitb; cgitb.enable()
print 1/0

The handler() method can Source: CoolInterview.com
Question: How do I read (or write) binary data?

Answer: or complex data formats, it's best to use the struct module. It allows you to take a string containing binary data (usually numbers) and convert it to Python objects; and vice versa.

For example, the following code reads two 2-byte integers and one 4-byte integer in big-endian format from a file:

import struct

f = open(filename, "rb") # Open in binary mode for portability
s = f.read(8)
x, y, z = struct.unpack(">hhl", s)


The '>' in the forma Source: CoolInterview.com
Question: How is python interpreted?

Answer: Python has an internal software mechanism which makes your programming easy. Program can run directly from the source code. Python translates the source code written by the programmer into intermediate language which is again translated it into the native language of computer. This makes it easy for a programmer to use python. Source: CoolInterview.com
Question: How do I create a multidimensional list?

Answer: You probably tried to make a multidimensional array like this:

A = [[None] * 2] * 3

This looks correct if you print it:

>>> A
[[None, None], [None, None], [None, None]]

But when you assign a value, it shows up in multiple places:

>>> A[0][0] = 5
>>> A
[[5, None], [5, None], [5, None]]

The reason is that replicating a list with * doesn't create copies, it only creates references to the existing objects. The *3 creat Source: CoolInterview.com
Question: How do I send mail from a Python script?


Answer: Use the standard library module smtplib.

Here's a very simple interactive mail sender that uses it. This method will work on any host that supports an SMTP listener.

import sys, smtplib

fromaddr = raw_input("From: ")
toaddrs = raw_input("To: ").split(',')
print "Enter message, end with ^D:"
msg = ''
while 1:
line = sys.stdin.readline()
if not line:
break
msg = msg + line

# The actual mail send
server = smtplib.SMTP('l Source: CoolInterview.com
Question: How do you make an array in Python?

Answer: Use a list:
["this", 1, "is", "an", "array"]

Lists are equivalent to C or Pascal arrays in their time complexity; the primary difference is that a Python list can contain objects of many different types.

The array module also provides methods for creating arrays of fixed types with compact representations, but they are slower to index than lists. Also note that the Numeric extensions and others define array-like structures with various characteristics as well.
Source: CoolInterview.com
Question: How do I use strings to call functions/methods?

Answer: There are various techniques.

* The best is to use a dictionary that maps strings to functions. The primary advantage of this technique is that the strings do not need to match the names of the functions. This is also the primary technique used to emulate a case construct:

def a():
pass

def b():
pass

dispatch = {'go': a, 'stop': b} # Note lack of parens for funcs

dispatch[get_input()]() # Note trailing parens to call function
*
Use t Source: CoolInterview.com
Question: How do I delete a file?

Answer: Use os.remove(filename) or os.unlink(filename); Source: CoolInterview.com
Question: How can I organize my code to make it easier to change the base class?

Answer: You could define an alias for the base class, assign the real base class to it before your class definition, and use the alias throughout your class. Then all you have to change is the value assigned to the alias. Incidentally, this trick is also handy if you want to decide dynamically (e.g. depending on availability of resources) which base class to use. Example:

BaseAlias = <real base class>
class Derived(BaseAlias):
def meth(self):
BaseAlias.meth(self) Source: CoolInterview.com
Question: When I edit an imported module and reimport it, the changes don't show up. Why does this happen?

Answer: For reasons of efficiency as well as consistency, Python only reads the module file on the first time a module is imported. If it didn't, in a program consisting of many modules where each one imports the same basic module, the basic module would be parsed and re-parsed many times. To force rereading of a changed module, do this:

import modname
reload(modname)

Warning: this technique is not 100% fool-proof. In particular, modules containing statements like

from modnam Source: CoolInterview.com
Question: Explain about the use of python for web programming?

Answer: Python can be very well used for web programming and it also has some special features which make you to write the programming language very easily. Some of the features which it supports are Web frame works, Cgi scripts, Webservers, Content Management systems, Web services, Webclient programming, Webservices, etc. Many high end applications can be created with Python because of the flexibility it offers. Source: CoolInterview.com

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