For python users (programming)?

Question

2 questions id like to ask

What is the difference between a tuple and a list?

What is the difference between a list and a dictionary?

Answer 1

As far as I know:

You can't modify tuple but you can modify list. This is should be more memory efficient.

List contains just variables that have position in that list (lis[0], lis[-1] ..) but in dictionary you don't have clear position for all variables but you can use other variables as keys ("bookmarks") for your variables. So you create a simple phonebook using:

phonebook = {'Mike':12345, 'Keke':98765, 'Mother': 98123}

now you can fetch Mikes number using phonebook['Mike']

Of course you can use other variables than strings as your keys:

tuple1= ('Dipum', 'Dipam', 'piupou')

tuple2 = ('Pitim', 'Pitam')

dictionary1 = {tuple1:'todii', tuple2:1233, 'magic':tuple1}

dictionary1[tuple1]

dictionary1[dictionary1['magic']]

If you think about it, there is clear reason why you can use tuples as keys but you can't use lists.

Answer 2

A tuple is not modified once created ; if you have a C programming background, then you can think of a tuple as an array of constant ; while a list is modifiable so it can be assigned new elements ot get its elements deleted .

Many functions return tuples as a return value , so that the caller for these functions wouldn't modify the result .

A list is just analogous to an array : It's indexes are numeric ( 0,1,2, ...).

You can think of a dictionary as a list whose indexes can be anything non numerical as long as these indexes are unmodifiable ( strings, tuples, numbers )

BTW, I answered ur other question regarding the countLines(), but seems that Yahoo Answers doesn't retain the indentation , which is essential for Python. So I am sending the same source BUT substitute EACH occurrence of the '@' symbol below with a space  so that you get the correct logical indentation for the program to run :P

import sys # for exit()

def countLines() :

@n=0 # to hold the number of lines

@try :

@@f = open ("somefile.txt") // use correct file name and path

@@for line in f :

@@@n = n +1

@@return n

@except :

@@print "File error. The program will end "

@@sys.exit()

numberofLines = countLines()

print 'The file ',numberofLines,'lines'

raw_input()