CODEWITHSUNDEEP
pythonoperators
Amy Rose
Amy Rose

Reputation: 95

And and Or confusion

I have a file I'm parsing, on each line in the same column are one of the values; 0, 1 or -1. I want to parse this so that the numeric values are all in line as below. I am trying to this via an if statement with and/or operators. I cannot get my head around the and/or as when I test this with a print statement, output either prints 1's or prints 0's.

 Desired output:
 0
 1
-1

if number.startswith('1' and '0'):
    return number.append(' ')
print number

Upvotes: 0

Views: 76

Answers (3)

Alex Andre
Alex Andre

Reputation: 1

Firstly, you're using .startswith with a coherent intention, but the arguments don't work that way, try this:

if number.startswith('1', '0'):

Secondly, .append does not do what you want. If you want to add a space in front of number if it begins with '1' or '0', try this:

if number.startswith('1', '0'):
    number = ' ' + number
print number

Additionally, .append is used to add an item to the end of a list, for example:

>>> list = [1, 2]
>>> list.append('x')
>>> list
[1, 2, 'x']

Upvotes: 0

Martijn Pieters
Martijn Pieters

Reputation: 1124998

'1' and '0' resolves to just '0':

>>> '1' and '0'
'0'

Boolean operators are not the same thing English grammatical constructs!

The str.startswith() method takes a tuple of values to test for:

number.startswith(('1', '0'))

and it'll return True if your string starts with '1' or it starts with '0'.

However, in this case you can just use string formatting to pad out your number:

return format(int(number), '-2d')

This pads your number out to a field two characters wide, leaving space for a negative sign:\

>>> format(-1, '-2d')
'-1'
>>> format(0, '-2d')
' 0'
>>> format(1, '-2d')
' 1'

Upvotes: 3

Cory Kramer
Cory Kramer

Reputation: 118021

The problem is that the expression '1' and '0' is being evaluated as a bool, and will evaluate to '0'. The whole expression will then be if number.startswith('0'): so the '1' is never being checked.

You should to change this

if number.startswith('1' and '0'):

To

if number.startswith('1') or number.startswith('0'):

Or

if number[0] in ('1', '0'):

Upvotes: 0

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