CODEWITHSUNDEEP
pythonpython-3.x
Joel
Joel

Reputation: 99

Python - Printing a list of lists with strings inbetween

I am trying to write a function that will take a list of lists and print them out one by one with the word UNION between them. My code looks like this:

def printsql(lst):
    print("INSERT INTO table")
    for x in lst:
        print("SELECT")
        print(*x, sep=', ')
        print("UNION")
    return(str)

a = [[1, 3, 4], [2, 5, 7], [3, 4, 6]]

print(printsql(a))

My output currently looks like this:

INSERT INTO table
SELECT
1, 3, 4
UNION
SELECT
2, 5, 7
UNION
SELECT
3, 4, 6
UNION

This is almost exactly what I need but I can't figure out how to not print the last "UNION". Can someone advise?

Upvotes: 2

Views: 1694

Answers (5)

dawg
dawg

Reputation: 103844

Consider using the .join method in Python to insert a string between list elements.

Works like so:

>>> '|'.join(['a','b','c','d'])
'a|b|c|d'

Your example is essentially doing this:

[Header string "INSERT INTO table\nSELECT\n"]
'\nUNION\nSELECT\n'.join([list items])
', '.join([sub list items])

To get the pattern you describe.

You can take that description and translate to Python:

def printsql(lst):
    s="INSERT INTO table\nSELECT\n"
    s+="\nUNION\nSELECT\n".join(', '.join(str(e) for e in sl) for sl in lst)
    return s

Then:

>>> a = [[1, 3, 4], [2, 5, 7], [3, 4, 6]]
>>> print(printsql(a))
INSERT INTO table
SELECT
1, 3, 4
UNION
SELECT
2, 5, 7
UNION
SELECT
3, 4, 6

The general outline is:

  1. Create the header with s="INSERT INTO table\nSELECT\n";
  2. Use a nested join to create the list of lists format of "\nUNION\nSELECT\n" between the outer list elements and ', ' with the inner list elements;
  3. Return the string to be printed or used in another section of the program.

Upvotes: 2

Ryan
Ryan

Reputation: 133

This will remove the last union and class str 

   def printsql(lst):
        print("INSERT INTO table")
        counter = 0
        for x in lst:
                counter = counter + 1
                print("SELECT")
                print(*x, sep=', ')
                if (len(lst)- 1) > counter:
                        print("UNION")
        return("")

a = [[1, 3, 4], [2, 5, 7], [3, 4, 6]]

print(printsql(a))

Upvotes: 1

Austin
Austin

Reputation: 26039

This is one way avoiding an extra looping and condition:

def printsql(lst):
    print("INSERT INTO table")
    for x in lst[:-1]:
        print("SELECT")
        print(*x, sep=', ')
        print("UNION")
    print("SELECT")
    print(*lst[-1], sep=', ')
    return(str)

a = [[1, 3, 4], [2, 5, 7], [3, 4, 6]]

print(printsql(a))

'''
INSERT INTO table
SELECT                                                      
1, 3, 4                                                     
UNION                                                      
SELECT                                                      
2, 5, 7                                                     
UNION                                                       
SELECT                                                     
3, 4, 6                                                    
<class 'str'>                                               
'''

Upvotes: 1

Jon Reinhold
Jon Reinhold

Reputation: 189

Quick and dirty. 

def printsql(lst):
    print("INSERT INTO table")
    for x in lst:
            if x != lst[-1]:
                 print("SELECT")
                 print(*x, sep=', ')
                 print("UNION")
            else:
                print("SELECT")
                print(*x, sep=', ')

    return(str)

a = [[1, 3, 4], [2, 5, 7], [3, 4, 6]]

print(printsql(a))

Upvotes: 0

Pam
Pam

Reputation: 1163

The brute force is to use enumerate

for idx, x in enumerate(lst):
  #other stuff#
  if idx<(len(lst) - 1):
    print("UNION")

But I’d be interested to see if there is a more elegant solution.

Upvotes: 3

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