how to fix if-else problem in calling functions in python?

Question

if file is not None:
        content = file.readlines()
        if 'I'  and 'J' in content:
            display_oval()
        else:
            display_polygon()

in this case,suppose i opened a file containing I&J . i expect to call display_oval() but it calls display_polygon(). when i opened file not containing I&J,display_polygon() calls as expected. when i replaced 'I' and 'J'with 'I' or 'J',when i opened a file containing I&J,display_oval() works fine. But when i opened file not containing I&J, nothing works. I want to call display_oval()if file contains I&J and display_polygon()otherwise. how it can be done?

Blckknght · Accepted Answer · 2021-06-11 05:22:54Z

1

You have a couple of intersecting issues with your code.

Thie first issue is that 'I' and 'J' in content gets grouped as ('I') and ('J' in content), which is surely not what you intend. A string like 'I' is always truthy, so testing in that way is not useful. You probably mean 'I' in content and 'J' in content`.

But that's not enough to fix your code (it makes fewer inputs match, not more). The condition will still not work right because your content is a list of strings, all but the last of which will be newline terminated. When done on a list, the in operator expects exact matches, not substring matches as in does when both arguments are strings.

I'm not exactly sure what fix would be best for that second issue. It depends on the logic of your program, and the contents of your file. If you want to test if I and J show up as individual lines in the file (each separately, on a line with no other characters), you might want to test for 'I\n' in content and 'J\n' in content using the same content you're using now. On the other hand, if you want to check for a capital I and J characters anywhere in the text of the file, without regard to lines, then you probably need to change content instead of changing the matching logic. Use content = file.read() to read the whole file into a single string, rather than a list of strings. Then 'I' in content will do a substring search.

answered Jun 11, 2021 at 5:22

Blckknght

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2 Comments

abdulla thahir Over a year ago

okay. my file consist of lines and each line consist of strings. content = file.readlines() for line in content: for i in line: if i == 'I' and 'J': display_oval() else: display_polygon() .i rewrite the code as this. But no change in result. Although i want to use readlines() for read file

Blckknght Over a year ago

i == 'I' and 'J' has the same issue I describe in my answer, the and operator doesn't distribute the equals like you seem to expect. From your description, it's unclear what you want to be checking for. Do you want to check if both letters are in the same line? Or both letters are in some line, somewhere in the file, but it doesn't need to be the same line. If you want to be searching for those characters anywhere in the file, using read() is a lot better than readlines(). You can get the results of the latter from the results of the former by calling splitlines() on the big string.

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