List operations in Python and list operations in Python

List operations in Python and list operations in Python

Python list operations are powerful and convenient (compared with Java)
Simple and regular operations will not be mentioned (this is not an introductory tutorial). We will introduce several examples with special features.

Add

# Append to the end (append) li = [1, 2, 3, 4, 5] li. append (6) print ('Li = % s' % li) # output: li = [1, 2, 3, 4, 5, 6] # append a list (extend) li2 = ['A', 'B', 'C', 'D', 'E'] li. extend (li2) print ('Li = % s' % li) # output: li = [1, 2, 3, 4, 5, 6, 'A ', 'B', 'C', 'D ', 'E'] # Add li_plus = li + li2print ('li _ plus = % s' % li_plus) to the list and list # output: li_plus = [1, 2, 3, 4, 5, 6, 'A', 'B', 'C', 'D', 'E', 'A', 'B', 'B', 'C ', 'D', 'E']

Delete

# Delete the element li = [1, 2, 3, 4, 5] li in the list. remove (3) print ('Li = % s' % li) # output: li = [1, 2, 4, 5]
# Delete the element del li [3] print ('Li = % s' % li) based on the index # output: li = [1, 2, 4]

 

Intercept (also called slice Operation)
Format: [start: end: step]. Remember this format and you will be able to make full use of your imagination.

Li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# Take a li2 = li [: 2] print ('li2 = % s' % li2) for every two elements # output: li2 = [0, 2, 4, 6, 8, 10] # last element = li [-1] print ('element = % s' % element) # output: element = 10 # copy (a new object after copying) li2 = list (li) print ('li2 = % s' % li2) # output: li2 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Extract and delete (pop)

Li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] # extract and delete the last element li. pop () # equivalent to li. pop (-1) print ('Li = % s' % li) # output: li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] # extract and delete the first element (or the nth element) li. pop (0) print ('Li = % s' % li) # output: li = [1, 2, 3, 4, 5, 6, 7, 8, 9]

 

Sort

# Li = [3, 1, 5, 8, 0, 9, 2, 6, 7, 4] li in the forward order. sort () print ('Li = % s' % li) # output: li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] # reverse li = [3, 1, 5, 8, 0, 9, 2, 6, 7, 4] li. sort (reverse = True) print ('Li = % s' % li) # output: li = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] # Flip (not in reverse order) li = [3, 1, 5, 8, 0, 9, 2, 6, 7, 4] li. reverse () print ('Li = % s' % li) # output: li = [4, 7, 6, 2, 9, 0, 8, 5, 1, 3]

List Parsing
Efficiently create a new list based on the existing list
Format: [expression for iter_val in iterable]

# Square li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] li2 = [I ** 2 for I in li] print ('li2 = % s' % li2) # output: li2 = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] # obtain the square of a number greater than 5. The expression can also be an if statement li = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] li2 = [I ** 2 if I> 5 else I for I in li] print ('li2 = % s' % li2) # output: li2 = [0, 1, 2, 3, 4, 5, 36, 49, 64, 81]

Format: [expr for iter_var in iterable if cond_expr]

# Only elements other than None, li = [0, 1, 2, 3, 4, 5, None, 6, 7, 8, 9] li2 = [I for I in li if I is not None] print ('li2 = % s' % li2) # output: li2 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Format: [expr for iter_var in iterable for var in iter_var]

# Expand a two-dimensional list li = [0, 1, 2], [3, 4, 5, 6], [7, 8, 9] li2 = [j for I in li for j in I] print ('li2 = % s' % li2) # output: li2 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Join)

Li = ['aaa', 'bbb ', 'ccc', 'ddd '] li2 = ','. join (li) print ('li2 = % s' % li2) # output: li2 = aaa, bbb, ccc, ddd