python strings list | python training in bangalore -learnbay.in
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Class4- String ,Lists
Class4www.learnbay.in - Python training in Bangalore
Strings
A String is sequence of character.
How to create a string?
# all of the following are equivalentmy_string = 'Hello'
my_string = "Hello"
my_string = '''Hello'''
# Multiple line either single triple quote or single double quote
my_string = """Hello, welcome to
the world of Python"""
del my_string
Strings ..
Print “\\”
Print r’\\’
print 'C:\\abcd'
print r'C:\\abcd'
Access Characters in string?
Strings are immutable.
Indexing: Access individual elements of string.
Index must be an integer.Accessing character out of index will raise “IndexError”
Python Allows negative indexing for its sequences
*****Try few negative indexes and figure out what negative index does*****
Output??
s = 'kri'
a,b,c=s
print a+b+c
print b
print c
Strings-Slicing
String = “abc ghijklm”
String[start:end:stride]
End is up to but not including the character at position end.
If start is omitted- defaults to 0
If end is omitted -defaults to end of string
If stride is omitted it defaults to 1
Do exercises on the above.Put end as -ve, stride as negative and then check
https://repl.it/FWyl/0 : Code example - String slicing
String: Operations
Try out “+,*,in and not in” on strings.
Try out these builtin methods:
capitalize() ,center(width, fillchar),
count(str, beg= 0,end=len(string)) : Counts how many times str occurs in string or in a substring of string
find(str, beg=0, end=len(string)) :Determine if str occurs in string or in a substring of string.Return index if
found else -1.
index(str, beg=0, end=len(string)): same as find but return exception if not found
https://repl.it/GFc2/8 : code example- String Methods
https://repl.it/FXnj/3: Reverse a string
List
List is a sequence of values.
Items in a list need not be of the same type.
list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"]
List4 = [‘a’,’b’,[1.0,2]]
Lists are mutable. Exercise:- Take a list and change/Update one member of list.
Also do some example on “in” operator in the list.
List …..
Delete from list:
list1 = ['physics', 'chemistry', 1997, 2000];
print list1
del list1[2];
print "After deleting value at index 2 : "
print list1
Try +,*,len ,in operations on list and also slicing on Lists.
t=[1,2,3,4,5] t[1:3]=[8,8] print t
Lists Methods
Try examples on theses methods:
Append ,extend ,sort,pop etc
Cmp,len,max,min etc
List Code example1: https://repl.it/FXmp/8
Example2: https://repl.it/FXkk/0
Example: https://repl.it/Hk1i/0
Example3; https://repl.it/GQlF/2 -Reverse list
LIst Comprehension
List Comprehension Provides a concise way to Create a list.
It Consists of brackets ,expressions followed by a for clause, then
zero or more for or if clauses.
Returns a new list
Basic Syntax is :
[ expression for item in list if conditional ]
Examples of List Comprehension
List = [i for i in range(10)]
squares = [x**2 for x in range(10)]
[x+y for x in [10,30,50] for y in [20,40,60]]
[x.upper() for x in ["a","b","c"]]
List Comprehension Code Example: https://repl.it/GQk9/3
List to str: https://repl.it/GQlO/1
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