I have a list `l`:

``````l = [22, 13, 45, 50, 98, 69, 43, 44, 1]
``````

For numbers above 45 inclusive, I would like to add 1; and for numbers less than it, 5.

I tried

``````[x+1 for x in l if x >= 45 else x+5]
``````

But it gives me a syntax error. How can I achieve an `if``else` like this in a list comprehension?

``````>>> l = [22, 13, 45, 50, 98, 69, 43, 44, 1]
>>> [x+1 if x >= 45 else x+5 for x in l]
[27, 18, 46, 51, 99, 70, 48, 49, 6]
``````

Do-something if `<condition>`, else do-something else.

The reason you’re getting this error has to do with how the list comprehension is performed.

Keep in mind the following:

``````[ expression for item in list if conditional ]
``````

Is equivalent to:

``````for item in list:
if conditional:
expression
``````

Where the `expression` is in a slightly different format (think switching the subject and verb order in a sentence).

Therefore, your code `[x+1 for x in l if x >= 45]` does this:

``````for x in l:
if x >= 45:
x+1
``````

However, this code `[x+1 if x >= 45 else x+5 for x in l]` does this (after rearranging the `expression`):

``````for x in l:
if x>=45: x+1
else: x+5
``````

``````[x+1 if x >= 45 else x+5 for x in l]
``````

And for a reward, here is the comment, I wrote to remember this the first time I did this error:

Python’s conditional expression is `a if C else b` and can’t be used as:

``````[a for i in items if C else b]
``````

The right form is:

``````[a if C else b for i in items]
``````

Even though there is a valid form:

``````[a for i in items if C]
``````

But that isn’t the same as that is how you filter by `C`, but they can be combined:

``````[a if tC else b for i in items if fC]
``````

You must put the expression at the beginning of the list comprehension, an if statement at the end filters elements!

``````[x+1 if x >= 45 else x+5 for x in l]
``````

Like in `[a if condition1 else b for i in list1 if condition2]`, the two `if`s with `condition1` and `condition2` doing two different things. The part `(a if condition1 else b)` is from a lambda expression:

``````lambda x: a if condition1 else b
``````

while the other `condition2` is another lambda:

``````lambda x: condition2
``````

Whole list comprehension can be regard as combination of `map` and `filter`:

``````map(lambda x: a if condition1 else b, filter(lambda x: condition2, list1))
``````

You can also put the conditional expression in brackets inside the list comprehension:

``````    l = [22, 13, 45, 50, 98, 69, 43, 44, 1]
print [[x+5,x+1][x >= 45] for x in l]
``````

[false,true][condition] is the syntax

I just had a similar problem, and found this question and the answers really useful. Here’s the part I was confused about. I’m writing it explicitly because no one actually stated it simply in English:

The iteration goes at the end.

Normally, a loop goes

``````for this many times:
if conditional:
do this thing
else:
do something else
``````

Everyone states the list comprehension part simply as the first answer did,

``````[ expression for item in list if conditional ]
``````

but that’s actually not what you do in this case. (I was trying to do it that way)

In this case, it’s more like this:

``````[ expression if conditional else other thing for this many times ]
``````

You could move the conditional to:

``````v = [22, 13, 45, 50, 98, 69, 43, 44, 1]
[ (x+1 if x >=45 else x+5)  for x in v ]
``````

But it’s starting to look a little ugly, so you might be better off using a normal loop. Note that I used `v` instead of `l` for the list variable to reduce confusion with the number 1 (I think `l` and `O` should be avoided as variable names under any circumstances, even in quick-and-dirty example code).