如何在一行中编写一个for循环和多个if语句？

Question

Is there a way to write something like this in one line?

for x in list: 
   if condition1: 
       (...) 
   elif condition2: 
       (...) 
   else: 
       (...) 

Another way of asking is: Is it possible to combine following list comprehensions?

(...) for x in list

and

123 if condition1 else 345 if condition2 else 0

Answer 1

What you want to do would almost certainly be considered bad style. Maybe it's an XY problem ? In that case, you should open another question with the underlying issue.

If you're sure this is what you want, have a look at the following example, using PEP 308 -- Conditional Expressions :

>>> def f(condition1, condition2):
...     return 1 if condition1 else 2 if condition2 else 3
... 
>>> f(True, False)
1
>>> f(True, True)
1
>>> f(False, True)
2
>>> f(False, False)
3

Subsequently, your example

for x in list: 
   if condition1: 
       (...) 
   elif condition2: 
       (...) 
   else: 
       (...) 

could be written as a list comprehension as follows:

[(...) if condition1 else (...) if condition2 else (...) for x in list]

Answer 2

use lsit comprehensions

var = [i for i in list if i == something or i == something] more on that here

Answer 3

Yes, there are ways, but not recommended. Here is an example of how you could do it:

l = [1,2,3,4,5,6,7]

for x in l:
  if x%2 == 0:
    print("Even")
  elif x%2 == 1:
    print("Odd")
  else:
    print("Nothing")

print("And here the one-liner:")

[print("Even") if x%2 == 0 else print("Odd") if x%2 == 1 else print("Nothing") for x in l]

I don't recommend this way, because of readability. Read The Zen of Python , don't make too long lines (max 80 characters)

Answer 4

The way to write for loop in a single line , mostly used in Data Science Project, You can use this way, as we have six labeled fake news LIAR:

Labels: ['barely-true' 'false' 'half-true' 'mostly-true' 'pants-fire' 'true'], to represent this as a binary labels:

We use the following way:

labels = [ 1 if lab=='false' or lab=='pants-fire' or lab=='barely_true'  else 0 for lab in df.is_fake]

Another way, the same if-else condition for loop :

labels = [ 1 if lab=='false' else 1 if lab=='pants-fire' else 1 if lab=='barely_true'  else 0 if lab == 'true' else 0 if lab == 'half-true' else 0 for lab in df.is_rumor]

Hope to help many of you, who want to do the same way in many problem-solving.