How to change to code to get an output of a float in a list

Question

I am trying to get a output of [3.1] where the number in the list is a float.

b = "3.1"
list1 = []
for i in b:
    list1.append(i)
print(list1)

I expect the output to be [3.1], but the code above outputs ['3', '.', '1']

Possible duplicate of [How do I parse a string to a float or int in Python?](https://stackoverflow.com/questions/379906/how-do-i-parse-a-string-to-a-float-or-int-in-python) — Sheldore, May 10 '19 at 07:44
Have you tried debugging your code? What does `i` contain in each iteration of your loop? — Nico Haase, May 10 '19 at 07:45
You need to cast your string as a float to append it to a list @ProgrammingWarrior check my answer below :) — Devesh Kumar Singh, May 16 '19 at 17:47

score 1 · Answer 1 · answered May 10 '19 at 07:42

for i in b: list1.append(i) means "for each character in the string b, append that character to the list list1", giving you exactly what you asked for: a three-character list.

If you just want to turn b into float and append to the list, this suffices:

list1.append(float(b))

score 0 · Answer 2 · answered May 10 '19 at 07:42

0

Try this :

list1 = [float(b)]

OUTPUT :

[3.1]

The reason you're getting a list like ['3', '.', '1'] is because you're iterating over all the characters of string b. You need to convert the string type of b to float and then append it to a list.

answered May 10 '19 at 07:42

Arkistarvh Kltzuonstev

6,824
7
26
56

score 0 · Answer 3 · answered May 10 '19 at 07:45

In the code, variable b is of format string. Convert it to float and append to list.

b = "3.1"
list_1 = []
list_1.append(float(b))
print (list_1)

This should give you the desired output.

The way you are doing, variable b is in string format. This makes the for loop append individual character to list that is respectively '3', '.', '1'. Conversion of string to float should solve your problem.

score 0 · Accepted Answer · answered May 10 '19 at 07:56

Let's see what is happening under the hood here

In [9]: b = "3.1"                                                                                                                                                                 

In [10]: for i in b: 
    ...:     print(i) 
    ...:                                                                                                                                                                          
3
.
1

As you can see, since b is a string, iterating over a string gives you individual characters of the string, which you end up appending to the list, and the list looks like ['3', '.', '1']

Hence you need to convert the string to a float, and then append it to the list, which is as simple as

In [11]: b = "3.1"                                                                                                                                                                

In [12]: [float(b)]                                                                                                                                                               
Out[12]: [3.1]

Here we convert b to a float, and create a single list element with 3.1 as it's only element

A similar idea can be applied when you are dealing with a list of strings and each string represents a float, where we convert every element to a float, and make a new list out of it

In [13]: b = [ "2.7", "2.9", "3.1"]                                                                                                                                               

In [14]: [float(i) for i in b]                                                                                                                                                    
Out[14]: [2.7, 2.9, 3.1]

How to change to code to get an output of a float in a list

4 Answers4