Python: Treating A Scalar As A One Element List

I am writing a python script that process lists read from a file: l = readListFromFile( myFile ) for i in l : # do something to each element All works fine when l has more tha

Solution 1:

Well a simple solution is

l = readListFromFile(myFile)
try:
    i = iter(l)
    ifisinstance(l, str):
        i = l 
except TypeError:
    i = [l]
for .... in i

This will work even if you change what readListFromFile to return another iterable.

A one liner solution if it's guaranteed to be a str or a list (or other iterable) is just

l = readListFromFile(myFile)
for e in [l] ifisinstance(l, str) else l:

just using a ternary operator.

On an aside, having a method called readList... not always returning a list is just evil.

Solution 2:

l = readListFromFile(myFile)
if isinstance(l, list):
    for i in l :
        # do something to each elementelse:#do that something mentioned above

or

l = readListFromFile(myFile)
ifisinstance(l, str):
    l = [l]
for i in l:
    #do that same something as above

or

l = readListFromFile(myFile)
try:
    for i in l:
        #do that somethingexcept:#do that something with the value

and if you want a function:

def get_me_a_list(var):
    if isinstance(var, list):
        returnvarreturn [var]

l = get_me_a_list(readListFromFile(myFile))
for i in l:
    #do your something

Solution 3:

Using a generator function and isinstance:

defsolve(lis):
   ifisinstance(lis, list):
      for item in lis:  #use just `yield from lis` in py3.xyield item
   else:
      yield lis

Demo:

>>>for item in solve(1):...print item...
1
>>>for item in solve([1, 2, 3]):
    print item
...
1
2
3

To handle any type of iterable you can use collections.Iterable:

from collections import Iterable
defsolve(lis):
   ifisinstance(lis, Iterable) andnotisinstance(lis, basestring):
      for item in lis:  #use just `yield from lis` in py3.xyield item
   else:
      yield lis

Solution 4:

You can put the check directly into the for-loop:

l = readListFromFile( myFile )
for i in (l if isinstance(l, list) else [l]):
    # Do something with i

Solution 5:

If readFromFile returns a scalar rather than a list, then you can turn it to a list by yourself.

l = readListFromFile( myFile )
if not isinstance(l, list):
    l = [l]
for i in l :
    # do something to each element