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Testing Strategies

  Testing Strategies 1. Importance of Testing Strategies    - Ensures correctness, completeness, and quality of software    - Identifies errors, gaps, and missing requirements    - Helps in reducing and removing errors to improve software quality    - Verifies if software meets specified requirements 2. Testing Techniques and Approaches    - Component-level testing to integration testing    - Different techniques suitable at different stages of testing    - Incremental testing approach for better effectiveness    - Involvement of both developers and independent test groups 3. Distinction between Testing and Debugging    - Testing focuses on finding errors and verifying requirements    - Debugging is the process of identifying and fixing errors    - Both activities are important but serve different purposes Topic: Benefits of Software Testing 1. Cost-Effectiveness    - Identifying bugs early saves money in the long run    - Fixing issues in the early stages is less expensive 2. Security

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Python - Dictionary

 Each key is separated from its value by a colon (:), the items are separated by commas, and the whole thing is enclosed in curly braces. An empty dictionary without any items is written with just two curly braces, like this: {}.

Keys are unique within a dictionary while values may not be. The values of a dictionary can be of any type, but the keys must be of an immutable data type such as strings, numbers, or tuples.

Accessing Values in Dictionary

To access dictionary elements, you can use the familiar square brackets along with the key to obtain its value. Following is a simple example −

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print "dict['Name']: ", dict['Name']
print "dict['Age']: ", dict['Age']

When the above code is executed, it produces the following result −

dict['Name']:  Zara
dict['Age']:  7

If we attempt to access a data item with a key, which is not part of the dictionary, we get an error as follows −

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
print "dict['Alice']: ", dict['Alice']

When the above code is executed, it produces the following result −

dict['Alice']:
Traceback (most recent call last):
   File "test.py", line 4, in <module>
      print "dict['Alice']: ", dict['Alice'];
KeyError: 'Alice'

Updating Dictionary

You can update a dictionary by adding a new entry or a key-value pair, modifying an existing entry, or deleting an existing entry as shown below in the simple example −

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School"; # Add new entry

print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']

When the above code is executed, it produces the following result −

dict['Age']:  8
dict['School']:  DPS School

Delete Dictionary Elements

You can either remove individual dictionary elements or clear the entire contents of a dictionary. You can also delete entire dictionary in a single operation.

To explicitly remove an entire dictionary, just use the del statement. Following is a simple example −

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
del dict['Name']; # remove entry with key 'Name'
dict.clear();     # remove all entries in dict
del dict ;        # delete entire dictionary

print "dict['Age']: ", dict['Age']
print "dict['School']: ", dict['School']

This produces the following result. Note that an exception is raised because after del dict dictionary does not exist any more −

dict['Age']:
Traceback (most recent call last):
   File "test.py", line 8, in <module>
      print "dict['Age']: ", dict['Age'];
TypeError: 'type' object is unsubscriptable

Note − del() method is discussed in subsequent section.

Properties of Dictionary Keys

Dictionary values have no restrictions. They can be any arbitrary Python object, either standard objects or user-defined objects. However, same is not true for the keys.

There are two important points to remember about dictionary keys −

(a) More than one entry per key not allowed. Which means no duplicate key is allowed. When duplicate keys encountered during assignment, the last assignment wins. For example −

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'}
print "dict['Name']: ", dict['Name']

When the above code is executed, it produces the following result −

dict['Name']:  Manni

(b) Keys must be immutable. Which means you can use strings, numbers or tuples as dictionary keys but something like ['key'] is not allowed. Following is a simple example −

#!/usr/bin/python

dict = {['Name']: 'Zara', 'Age': 7}
print "dict['Name']: ", dict['Name']

When the above code is executed, it produces the following result −

Traceback (most recent call last):
   File "test.py", line 3, in <module>
      dict = {['Name']: 'Zara', 'Age': 7};
TypeError: unhashable type: 'list'

Built-in Dictionary Functions & Methods

Python includes the following dictionary functions −

Sr.No.Function with Description
1cmp(dict1, dict2)

Compares elements of both dict.

2len(dict)

Gives the total length of the dictionary. This would be equal to the number of items in the dictionary.

3str(dict)

Produces a printable string representation of a dictionary

4type(variable)

Returns the type of the passed variable. If passed variable is dictionary, then it would return a dictionary type.

Python includes following dictionary methods −

Sr.No.Methods with Description
1dict.clear()

Removes all elements of dictionary dict

2dict.copy()

Returns a shallow copy of dictionary dict

3dict.fromkeys()

Create a new dictionary with keys from seq and values set to value.

4dict.get(key, default=None)

For key key, returns value or default if key not in dictionary

5dict.has_key(key)

Returns true if key in dictionary dictfalse otherwise

6dict.items()

Returns a list of dict's (key, value) tuple pairs

7dict.keys()

Returns list of dictionary dict's keys

8dict.setdefault(key, default=None)

Similar to get(), but will set dict[key]=default if key is not already in dict

9dict.update(dict2)

Adds dictionary dict2's key-values pairs to dict

10dict.values()

Returns list of dictionary dict's values

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