Python - Lecture 4

Python
Lecture 4Lecture 4
- Ravi Kiran Khareedi

Lists - Revisited
• Accessing Values in List
list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5, 6, 7 ]list2 = [1, 2, 3, 4, 5, 6, 7 ]
print "list1[0]: ", list1[0]
print "list2[1:5]: ", list2[1:5]

Lists - Revisited
• Updating Values in List
list = ['physics', 'chemistry', 1997, 2000];
print "Value available at index 2 : "print "Value available at index 2 : "
print list[2];
list[2] = 2001;
print "New value available at index 2 : "
print list[2];

Lists – Revisted
• Deleting the entire list
Testlist = [‘a’, ’b’, ’c’]
print Testlistprint Testlist
del Testlist
print Testlist

Built in Functions
SN Function with Description
1
cmp(list1, list2)
Compares elements of both lists.
2
len(list)
Gives the total length of the list.
3
max(list)
Returns item from the list with max value.
4
min(list)
Returns item from the list with min value.
Output of cmp: cmp(list1, list2) - returns 0 if list1 = list2
returns 1 if list1 > list2
return -1 if list1 < list2
Others functions are self explanatory.
(These built in functions are supported by python for any kind of data structure not just lists)
4
Returns item from the list with min value.
5
list(seq)
Converts a tuple into list.
6
type(obj)
Returns the type of the object

More List Methods
list.append(obj) - Appends object obj to list
list.count(obj) - Returns count of how many times obj occurs in list
list.extend(seq) - Appends the contents of seq to list
list.index(obj) - Returns the lowest index in list that obj appears
list.insert(index,obj) - Inserts object obj into list at offset indexlist.insert(index,obj) - Inserts object obj into list at offset index
list.pop(obj = list[-1]) - Removes and returns last object or obj from list
list.remove(obj) - Removes object obj from list
list.reverse() - Reverses objects of list in place
list.sort() - Sorts objects of list, use compare func if given

Tuples - Revisited
• Accessing Values in Tuples
tup1 = ('physics', 'chemistry', 1997, 2000);
tup2 = (1, 2, 3, 4, 5, 6, 7 );
print "tup1[0]: ", tup1[0]print "tup1[0]: ", tup1[0]
print "tup2[1:5]: ", tup2[1:5]

Tuples - Revisited
• Updating Values in Tuples
Tuples are immutable so we cannot update them or change
values of tuple elements.
But we able to take portions of an existing tuples to create a
new tuples.new tuples.
Ex:
tup1 = (12, 34.56);
tup2 = ('abc', 'xyz');
tup3 = tup1 + tup2;
print tup3;

Tuples - Revisted
• Deleting Elements from tuples
– Not possible as its immutable.
– But the entire tuples can be deleted.
Ex:Ex:
tup = ('physics', 'chemistry', 1997, 2000);
print tup; del tup;
print "After deleting tup "
print tup;

More Tuple operations
Python Expression Results Description
len((1, 2, 3)) 3 Length
(1, 2, 3) + (4, 5, 6) (1, 2, 3, 4, 5, 6) Concatenation
('Hi!‘,) * 4 ('Hi!', 'Hi!', 'Hi!', 'Hi!') Repetition
3 in (1, 2, 3) True Membership
for x in (1, 2, 3): print x, 1 2 3 Iteration

Built in Tuple functions
1
cmp(tuple1, tuple2)
Compares elements of both tuples.
2
len(tuple)
Gives the total length of the tuple.
3
max(tuple)
Returns item from the tuple with max value.
3
Returns item from the tuple with max value.
4
min(tuple)
Returns item from the tuple with min value.
5
tuple(seq)
Converts a list into tuple.
6
type(obj)
Returns the type of the object

Dictionary – Revisted
• Accessing and Updating – Already seen
• Deleting Dictionary Elements
– Del dict(‘Key’) # remove the element with key
– dict.clear()
– del dict
Ex:
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print dict['Name'];
dict.clear();
print dict;
dict['Age'] = 25
print dict
del dict
dict['Name'] = “Muller“
TRY IT:
dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'}; # Key is not unique
print "dict['Name']: ", dict['Name'];

Built in Dictionary Functions
1
cmp(dict1, dict2)
Compares elements of both dict.
2
len(dict)
Gives the total length of the dictionary. This would be equal
to the number of items in the dictionary.
str(dict)
3
str(dict)
Produces a printable string representation of a dictionary
4
type(variable)
Returns the type of the passed variable. If passed variable is
dictionary, then it would return a dictionary type.
Note: Min and Max can also be applied to a dictionary but it returns the
minimum key value based on ASCII. So its of No Practical Use

More Dictionary Methods
SN Methods with Description
1
dict.clear()
Removes all elements of dictionary dict
2
dict.copy()
Returns a shallow copy of dictionary dict
4
dict.get(key, default=None)
For key key, returns value or default if key not in dictionary
5
dict.has_key(key)
Returns true if key in dictionary dict, false otherwise
6
dict.items()
Returns a list of dict's (key, value) tuple pairs
7
dict.keys()
Returns list of dictionary dict's keys
9
dict.update(dict2)
Adds dictionary dict2's key-values pairs to dict
10
dict.values()
Returns list of dictionary dict's values

Strings - Revisited
• String Special Operators:
a = “Hello”; b = “Python”

References
• http://www.tutorialspoint.com/python/

Python - Lecture 4

More Related Content

What's hot (20)

Similar to Python - Lecture 4 (20)

More from Ravi Kiran Khareedi (11)

Recently uploaded (20)

Python - Lecture 4