#Python unpacking sequence in item how to#

Longest_string_in_list.py Don’t call len twice!ġ7 Elegant way using map longest_string_in_list2. Top 4 of the grades are: Average grade: 8.17ġ6 Unelegant way of finding length of longest string Want to compare to top‘s N’th element, so top must be initialized with N values Make sure any value can enter top topN.py top 11 10 5 4 n 5 iġ4 Output topN.py - current top4: Top 3 of the grades are: Average grade: 5ġ0 Explanation passing_lists_to_functions.py grades 5 11 13ġ1 Explanation passing_lists_to_functions.py a grades 5 11ġ2 Better way of finding topN from a list of numbersĪlgorithm: Don’t find the max N times: Inefficient! Keep a sorted list of current top-N Go through given list one number at a time If number is greater than current N’th greatest, insert in correct positionġ3 Better way of finding topN from a list of numbers Passing_lists_to_functions.py sum and max functions To learn more about Python programming, you can read this article on tuple comprehension in Python. In dictionaries, only the keys of the dictionary are unpacked when using the unpacking operator.

The unpacking operation works the same in lists, sets, and tuples.

#Python unpacking sequence in item how to#

Lists are mutable, tuples are immutable > aList = > aList = 141 > aList > aTuple = (3, 6, 9) > aTuple = 141 Traceback (most recent call last): File '', line 1, in ? TypeError: object doesn't support item assignmentĨ Passing a list as an argument to a function In this article, we discussed how to use the unpacking operator in Python. 5.1 Sequence with elements and indices.Ħ Adding items to a list aList = # create empty list # add values to list for number in range( 1, 11 ): aList += Adds the values to the list (by adding a new list with one element to the existing list in each round) Using the + operator, you need to add a list to a list: aList += Using the append method, you add an element to the list: aList.append( number )ħ Using Lists and Tuples Only difference between lists and tuples is: Indexing as with slicing: “From a up to but not including b” > xrange(3, 12) > xrange(5) > xrange(1, 10, 2) > xrange(10, 1, -3) > ĥ Sequences -45 6 72 1543 -89 62 -3 1 6453 -78 c c cħ2 1543 -89 62 -3 1 6453 -78 c c c c c c c c c c c c Position number of the element within sequence c Name sequence (c) c c c c c c c c c c c c Fig. Startlist = # long list for i, name in enumerate( startlist ): # here we get both the subscript and the item: print “%s has index %d” %( name, i ) for name in startlist: # here we get the item directly, but not the subscript print nameĤ The xrange function The built-in xrange function returns a list

? Two ways of accessing all elements in a sequence Use brackets list1 = list2 = Tuples Use parentheses tuple1 = () Tuple2 = 5, tuple3 = ( 19, 27 )ģ for item in. Lists mutable Tuples immutable Sequence elements can be indexed with subscripts First index is 0 Access element with sequenceName Subscripts may be negative Slicing works same way as with stringsĢ Creating Sequences Creations Strings Lists Tuples Use quotes: s = ''

1 Sequences A sequence is a list of elements Lists and tuples