day-23 at payilagam [Lists]

what is list:

In Python, a list is a built-in dynamic sized array (automatically grows and shrinks) that is used to store an ordered collection of items. We can store all types of items (including another list) in a list. A list may contain mixed type of items, this is possible because a list mainly stores references at contiguous locations and actual items maybe stored at different locations.

here list is mutable and string is immutable

student_data = ['Guru Prasanna', 'B.Com', 21, True, 5.6]

print(student_data)

output:
['Guru Prasanna', 'B.Com', 21, True, 5.6]

Enter fullscreen mode Exit fullscreen mode

• list is a collection of data
• list has heterogeneous(various)data
• list is index based

student_data = ['Guru Prasanna', 'B.Com', 21, True, 5.6]

i = 0 
while i<len(student_data):
    print(student_data[i],end=' ')
    i+=1


output:
Guru Prasanna B.Com 21 True 5.6 

Enter fullscreen mode Exit fullscreen mode

in for loop:

for data in student_data:
    print(data)

Enter fullscreen mode Exit fullscreen mode

student_data = ['Guru Prasanna', 'B.Com', 21, True, 5.6]
index=0
for index,data in enumerate(student_data):
    print(index,data)
    index+=1

output:
0 Guru Prasanna
1 B.Com
2 21
3 True
4 5.6

Enter fullscreen mode Exit fullscreen mode

enumerate method index the values.

student_data = ['Guru Prasanna', 'B.Com', 21, True, 5.6]

print(student_data)

student_data[1] = 'M.Com'

print(student_data)

output:
['Guru Prasanna', 'B.Com', 21, True, 5.6]
['Guru Prasanna', 'M.Com', 21, True, 5.6]

Enter fullscreen mode Exit fullscreen mode

just removes and adds the new position value what we have just coded. we have to mention which positional value.

employee = []
employee.append('Raja')
employee.append('Madurai')
employee.append('B.Sc.,')
employee.append(5.2)
employee.append(True)

print(employee)

output:
['Raja', 'Madurai', 'B.Sc.,', 5.2, True]

Enter fullscreen mode Exit fullscreen mode

It is called as empty list.By,append method it
appends the value of the list.

employee.insert(2,'Tamilnadu')
print(employee)

employee.remove('Madurai') 
print(employee)

employee.pop(3) 
print(employee)

output:
['Raja', 'Madurai', 'Tamilnadu', 'B.Sc.,', 5.2, True]
['Raja', 'Tamilnadu', 'B.Sc.,', 5.2, True]
['Raja', 'Tamilnadu', 'B.Sc.,', True]
['Raja', 'Tamilnadu', 'B.Sc.,', True]

Enter fullscreen mode Exit fullscreen mode

In this case,append means adding at the end and insert means inbetween the values as we are giving specific index to fit the value.

• remove(value based removal)
• pop(index based removal)

l = [10,20,30,40,50,60]
del l[2]
print(l)

output:
[10, 20, 40, 50, 60]


l = [10,20,30,40,50,60]
del l[2:4]
print(l)

output:
[10, 20, 50, 60]


l = [10,20,30,40,50,60]

print(l.pop(2))

output:
30

Enter fullscreen mode Exit fullscreen mode

in first case del is a keyword,
in second case we are using indexing
in third case we are taking out second index and printing it out.

l = [10,20,30,40,50,60]
print(l)
print(l.pop(2))
print(l)
print(l.pop())
print(l)
print(l.pop(123))


output:
[10, 20, 30, 40, 50, 60]
30
[10, 20, 40, 50, 60]
60
[10, 20, 40, 50]
Traceback (most recent call last):
  File "/home/main.py", line 15, in <module>
    print(l.pop(123))
IndexError: pop index out of range

Enter fullscreen mode Exit fullscreen mode

in this case, pop(2) takes the index value and prints the value.
pop() prints the value of the last.
pop(123) prints error. there is no value assigned to it.

l = [10,20,30,40,50,60]
print(l)
del l[:] # del l
print(l)


output:
[10, 20, 30, 40, 50, 60]
[]

Enter fullscreen mode Exit fullscreen mode

after adding del keyword without any indexing inside it deletes everything and gives an empty list.

data_list = ['abcd','pqrs','xyz',1234, 1.234,True]
for data in data_list:
    if isinstance(data,str):
        print(data.upper())

output:
ABCD
PQRS
XYZ

Enter fullscreen mode Exit fullscreen mode

task:

names_list = ['sachin','dhoni','rohit','virat']

for name in names_list:
    if len(name)==5:
        print(name,end=' ')
print()

for name in names_list:
    if name[-1] == 't':
        print(name,end=' ')
print()

Output:

dhoni rohit virat 
rohit virat 

Enter fullscreen mode Exit fullscreen mode

原文链接：day-23 at payilagam [Lists]