Using Python String Formatting with Lists
Question:
I construct a string s in Python 2.6.5 which will have a varying number of %s tokens, which match the number of entries in list x. I need to write out a formatted string. The following doesn’t work, but indicates what I’m trying to do. In this example, there are three %s tokens and the list has three entries.
s = '%s BLAH %s FOO %s BAR'
x = ['1', '2', '3']
print s % (x)
I’d like the output string to be:
1 BLAH 2 FOO 3 BAR
Answers:
print s % tuple(x)
instead of
print s % (x)
You should take a look to the format method of python. You could then define your formatting string like this :
>>> s = '{0} BLAH BLAH {1} BLAH {2} BLAH BLIH BLEH'
>>> x = ['1', '2', '3']
>>> print s.format(*x)
'1 BLAH BLAH 2 BLAH 3 BLAH BLIH BLEH'
Following this resource page, if the length of x is varying, we can use:
', '.join(['%.2f']*len(x))
to create a place holder for each element from the list x. Here is the example:
x = [1/3.0, 1/6.0, 0.678]
s = ("elements in the list are ["+', '.join(['%.2f']*len(x))+"]") % tuple(x)
print s
>>> elements in the list are [0.33, 0.17, 0.68]
Since I just learned about this cool thing(indexing into lists from within a format string) I’m adding to this old question.
s = '{x[0]} BLAH {x[1]} FOO {x[2]} BAR'
x = ['1', '2', '3']
print (s.format (x=x))
Output:
1 BLAH 2 FOO 3 BAR
However, I still haven’t figured out how to do slicing(inside of the format string '"{x[2:4]}".format...,) and would love to figure it out if anyone has an idea, however I suspect that you simply cannot do that.
This was a fun question! Another way to handle this for variable length lists is to build a function that takes full advantage of the .format method and list unpacking. In the following example I don’t use any fancy formatting, but that can easily be changed to suit your needs.
list_1 = [1,2,3,4,5,6]
list_2 = [1,2,3,4,5,6,7,8]
# Create a function that can apply formatting to lists of any length:
def ListToFormattedString(alist):
# Create a format spec for each item in the input `alist`.
# E.g., each item will be right-adjusted, field width=3.
format_list = ['{:>3}' for item in alist]
# Now join the format specs into a single string:
# E.g., '{:>3}, {:>3}, {:>3}' if the input list has 3 items.
s = ','.join(format_list)
# Now unpack the input list `alist` into the format string. Done!
return s.format(*alist)
# Example output:
>>>ListToFormattedString(list_1)
' 1, 2, 3, 4, 5, 6'
>>>ListToFormattedString(list_2)
' 1, 2, 3, 4, 5, 6, 7, 8'
Here is a one liner. A little improvised answer using format with print() to iterate a list.
How about this (python 3.x):
sample_list = ['cat', 'dog', 'bunny', 'pig']
print("Your list of animals are: {}, {}, {} and {}".format(*sample_list))
Read the docs here on using format().
The same as @neobot’s answer but a little more modern and succinct.
>>> l = range(5)
>>> " & ".join(["{}"]*len(l)).format(*l)
'0 & 1 & 2 & 3 & 4'
x = ['1', '2', '3']
s = f"{x[0]} BLAH {x[1]} FOO {x[2]} BAR"
print(s)
The output is
1 BLAH 2 FOO 3 BAR
I construct a string s in Python 2.6.5 which will have a varying number of %s tokens, which match the number of entries in list x. I need to write out a formatted string. The following doesn’t work, but indicates what I’m trying to do. In this example, there are three %s tokens and the list has three entries.
s = '%s BLAH %s FOO %s BAR'
x = ['1', '2', '3']
print s % (x)
I’d like the output string to be:
1 BLAH 2 FOO 3 BAR
print s % tuple(x)
instead of
print s % (x)
You should take a look to the format method of python. You could then define your formatting string like this :
>>> s = '{0} BLAH BLAH {1} BLAH {2} BLAH BLIH BLEH'
>>> x = ['1', '2', '3']
>>> print s.format(*x)
'1 BLAH BLAH 2 BLAH 3 BLAH BLIH BLEH'
Following this resource page, if the length of x is varying, we can use:
', '.join(['%.2f']*len(x))
to create a place holder for each element from the list x. Here is the example:
x = [1/3.0, 1/6.0, 0.678]
s = ("elements in the list are ["+', '.join(['%.2f']*len(x))+"]") % tuple(x)
print s
>>> elements in the list are [0.33, 0.17, 0.68]
Since I just learned about this cool thing(indexing into lists from within a format string) I’m adding to this old question.
s = '{x[0]} BLAH {x[1]} FOO {x[2]} BAR'
x = ['1', '2', '3']
print (s.format (x=x))
Output:
1 BLAH 2 FOO 3 BAR
However, I still haven’t figured out how to do slicing(inside of the format string '"{x[2:4]}".format...,) and would love to figure it out if anyone has an idea, however I suspect that you simply cannot do that.
This was a fun question! Another way to handle this for variable length lists is to build a function that takes full advantage of the .format method and list unpacking. In the following example I don’t use any fancy formatting, but that can easily be changed to suit your needs.
list_1 = [1,2,3,4,5,6]
list_2 = [1,2,3,4,5,6,7,8]
# Create a function that can apply formatting to lists of any length:
def ListToFormattedString(alist):
# Create a format spec for each item in the input `alist`.
# E.g., each item will be right-adjusted, field width=3.
format_list = ['{:>3}' for item in alist]
# Now join the format specs into a single string:
# E.g., '{:>3}, {:>3}, {:>3}' if the input list has 3 items.
s = ','.join(format_list)
# Now unpack the input list `alist` into the format string. Done!
return s.format(*alist)
# Example output:
>>>ListToFormattedString(list_1)
' 1, 2, 3, 4, 5, 6'
>>>ListToFormattedString(list_2)
' 1, 2, 3, 4, 5, 6, 7, 8'
Here is a one liner. A little improvised answer using format with print() to iterate a list.
How about this (python 3.x):
sample_list = ['cat', 'dog', 'bunny', 'pig']
print("Your list of animals are: {}, {}, {} and {}".format(*sample_list))
Read the docs here on using format().
The same as @neobot’s answer but a little more modern and succinct.
>>> l = range(5)
>>> " & ".join(["{}"]*len(l)).format(*l)
'0 & 1 & 2 & 3 & 4'
x = ['1', '2', '3']
s = f"{x[0]} BLAH {x[1]} FOO {x[2]} BAR"
print(s)
The output is
1 BLAH 2 FOO 3 BAR