Line-breaking Expression in Python

Question

I am beginner in python and facing this problem. So how i can break the below expression in 2-3 lines

totalIncome = (classACost * float(classASeatsSold)) + (classBCost * float(classBSeatsSold)) + (classCCost * float(classCSeatsSold))

Like this.

totalIncome = (classACost * float(classASeatsSold)) +

(classBCost * float(classBSeatsSold)) + 

(classCCost * float(classCSeatsSold))

Basic reason is i wanted to fit the line in 80 columns. And if i am not right about question Title please also suggest suitable title. Thanks in advance.

A better title would be 'Line continuation in Python'. But if you had known that you would already have found the answer by googling: http://www.google.com/search?q=line+continuation+in+python — Mark Byers, Nov 27 '09 at 17:38
Well if i really know what i have to "Google" i would have done that. Thanks anyway for suggestion. — itsaboutcode, Nov 27 '09 at 17:39
Duplicate: http://stackoverflow.com/questions/53162/how-can-i-do-a-line-continuation-of-code-in-python — gnovice, Dec 08 '09 at 18:34

score 14 · Answer 1 · answered Nov 27 '09 at 17:45

You always never have to use line continuation characters in python thanks to parentheses:

totalIncome = ( (classACost * float(classASeatsSold)) +
                (classBCost * float(classBSeatsSold)) +
                (classCCost * float(classCSeatsSold)) )

Which gives you the advantage of not having to remove the character in case you join the lines later. Same goes for strings:

longString = ( 'This is the one line '
               'being continued here and '
               'ending with a line break \n' )

You almost always can use parentheses instead of line continuation symbols and it just looks nicer.

Also works list/dictionary definitions with brackets and braces respectively. — Adam Rosenfield, Nov 27 '09 at 17:46

Mark Byers · Accepted Answer · 2009-11-27T18:23:15.560

4

Put your expression in parentheses:

totalIncome = ((classACost * float(classASeatsSold)) +
    (classBCost * float(classBSeatsSold)) +
    (classCCost * float(classCSeatsSold)))

edited Nov 27 '09 at 18:23

answered Nov 27 '09 at 17:36

Mark Byers

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Thanks man. And one more thing, if i have long string in print(), how i can break it, because if i use "\n" its put 4 more spaces. Like this print("print\ google") – itsaboutcode Nov 27 '09 at 17:38
Split the string into smaller pieces. You can write it as print("long " + "string") and then put the new line after the plus. – Mark Byers Nov 27 '09 at 17:44
You don't even have to insert a `+`, see my answer. – Otto Allmendinger Nov 27 '09 at 17:46
2

-1: Backslashes are a last resort, parentheses are officially preferred in this example (see PEP 8), so this is poor advice. – nikow Nov 27 '09 at 18:21
OK, thanks for the notice. I updated the comment, based on your input. – Mark Byers Nov 27 '09 at 18:23

score 4 · Answer 3 · answered Nov 27 '09 at 17:47

I despise breaking a line over into several lines using 'backslashes'. By wrapping the entire expression on the right hand side of the equals character, you can break the lines without worrying about ensuring there is trailing whitespace or not, such as:

totalIncome = ((classACost * float(classASeatsSold)) + 
        (classBCost * float(classBSeatsSold)) + 
        (classCCost + float(classCSeatsSold)))

score 1 · Answer 4 · answered Nov 27 '09 at 23:46

Just in case you revisit the scene:

You have excessive parentheses already. You also have unnecessary occurrences of float() ... if a cost is a float and a seatsSold is an int, then you don't need float() at all.

Instead of

totalIncome = (classACost * float(classASeatsSold)) + (classBCost * float(classBSeatsSold)) + (classCCost * float(classCSeatsSold))

you could have

totalIncome = classACost * classASeatsSold + classBCost * classBSeatsSold + classCCost * classCSeatsSold

which can be wrapped as

totalIncome = (
       classACost * classASeatsSold
     + classBCost * classBSeatsSold
     + classCCost * classCSeatsSold
    )

or

totalIncome = (classACost * classASeatsSold
     + classBCost * classBSeatsSold
     + classCCost * classCSeatsSold)

or whatever reasonable style takes your fancy. Splitting at some fixed limit is IMHO not reasonable:

totalIncome = (classACost * classASeatsSold + classBCost * classBSeatsSold + 
    classCCost * classCSeatsSold)

I prefer the first because it screams "Generalise me!" ...

total_income = sum(seat_price[c] * seats_sold[c] for c in class_codes)

Line-breaking Expression in Python

4 Answers4