Reading comma-separated tuples from a file in python

Question

I am trying to read from a file with several tuples separated by commas. A sample input file looks like this:

(0, 0), (0, 2), (0, 4), (-1, -1), (0, -2), (1, -1), (-1, -3), (1 , 1), (-1, 3), (1, 1), (1, 3), (1, 5), (2, 0), (2, 2), (3, 3),

(2, 4), (3, 5), (4, 4), (5, 3), (6, 4), (5, 5), (7, 5)

After reading from this file, I need a tuple like this:

G = ((0, 0), (0, 2), (0, 4), (-1, -1), (0, -2), (1, -1), (-1, -3), \ (-1, 1), (-1, 3), (1, 1), (1, 3), (1, 5), (2, 0), (2, 2), (3, 3), \ (2, 4), (3, 5), (4, 4), (5, 3), (6, 4), (5, 5), (7, 5)) 

How can this be done effectively? Regards.

Answer 1

Since they look like proper python tuples, you can use literal_eval . Its fast as safe:

It is safe to evaluate a node expression or a string containing a Python expression. The string or node provided can only consist of the following Python literary structures: strings, numbers, tuples, lists, dicts, booleans, and None.

 import ast s = '''(0, 0), (0, 2), ...''' result = ast.literal_eval('({0})'.format(s)) 

Answer 2

Assuming file.txt exists with the following contents:

 (0, 0), (0, 2), (0, 4), (-1, -1), (0, -2), (1, -1), (-1, -3) (-1, 1), (-1, 3), (1, 1), (1, 3), (1, 5), (2, 0), (2, 2), (3, 3), (2, 4), (3, 5), (4, 4), (5, 3), (6, 4), (5, 5), (7, 5) 

You can use literal_eval() for each line in the loop and expand the resulting list:

 from ast import literal_eval result = [] with open('file.txt', 'r') as f: for line in f: result.extend(literal_eval(line.strip())) print result 

prints:

 [(0, 0), (0, 2), (0, 4), (-1, -1), (0, -2), (1, -1), (-1, -3), (-1, 1), (-1, 3), (1, 1), (1, 3), (1, 5), (2, 0), (2, 2), (3, 3), (2, 4), (3, 5), (4, 4), (5, 3), (6, 4), (5, 5), (7, 5)] 

FYI, literal_eval () is safe:

It is safe to evaluate a node expression or a string containing a Python expression. The string or node provided can only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None.

Hope this helps.