Convert string to list?

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Question :

I needed to pass%% of type:

0.4350    0.8798    0.0099         1

for a string

[0.4350, 0.8798, 0.0099, 1]

with a simple list . How can I do this?


Answer :

If you have a string with “0.4350 0.8798 0.0099 1”, you need to do two operations: separate the elements where there is white space, and for each separate element, which will be a string, transform it into a float number.

The first operation will always be done by the “split” method of strings in Python. By default this method still has the advantage of considering any number of whitespace (and other spacing characters such as newline, tabs, etc …) as a single space:

>>> a = "0.4350    0.8798    0.0099         1"
>>> b = a.split()
>>> b
['0.4350', '0.8798', '0.0099', '1']

For those of you in the first steps in Python, the easiest way to understand the second operation is to create a blank list, and for than for each element in b add its converted value to float in new list:

>>> c = []
>>> for elemento in b:
...     c.append(float(elemento))
>>> c
[0.435, 0.8798, 0.0099, 1.0]

But as people become more comfortable with Python, the ideal thing to do is to use a list comprehension – it’s an expression of Pythonq sitnaxe that lets you create a list from an arbitrary sequence using% on the same line – as an expression. Your entire problem would be solved like this:

c = [float(elemento) for elemento in "0.4350    0.8798    0.0099         1".split()]

(The contents of c will be the same as in the previous example).
What this form does: first you execute the expression that “for” will use, after the “in” – this is your initial string (which can be in a variable, of course), with the for method. Then the split is executed, and for each part of the sequence returned by the split, the expression before for , for is executed, and its result becomes part of the final list assigned to variable float(elemento) .

Finally, people who do not know Python well, but who are familiar with languages that allow a “functional” approach, can present solutions using the Python map, which is a built-in function that receives as parameters a function and a sequence, it automatically processes all the elements of the last sequence in the function – and creates a new output sequence. In Python version 2, the output of the map was a direct list – in Python 3, c creates a generator, which must be transformed into a list:

c = list(map(float, "0.4350    0.8798    0.0099         1".split()))

The version with list-comprehension is generally more expressive and easier to “think” than the approach to functional syntax – but does not prevent personal taste from using map . >

I’m not a developer , but I managed to solve it this way :

Python version 2x

Code :

str = '0.4350    0.8798    0.0099         1';
val = filter(None, str.split(' '));
print val

Output :

['0.4350', '0.8798', '0.0099', '1']

Online Example IDEONE

Python version 3x

def noEmpty(x):
    return x != ""
str = '0.4350    0.8798    0.0099         1';
print (list(filter(noEmpty, str.split(' '))));

OnLine Example IDEONE

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