How to use comparison and if not in python

Question

In one piece of my program I doubt if i use the comparison correctly  i want to make sure that   u0  lt   u  lt  u0 step   before do something    if not  u0  lt   u  and  u  lt  u0 step       u0   u0  step   change the condition until it is satisfied else      do something    condition is satisfied

User · Answer

Operator precedence in python
You can see that not X has higher precedence than and. Which means that the not only apply to the first part (u0 <= u). Write:

if not (u0 <= u and u < u0+step):

or even

if not (u0 <= u < u0+step):

User · Answer

Why think   If not confuses you  switch your if and else clauses around to avoid the negation        i want to make sure that   u0  lt   u  lt  u0 step   before do sth    Just write that   if u0  lt   u  lt  u0 step       do sth    What language is  sth    No vowels   An odd-looking word  else      u0   u0  step   Why overthink  it     If you need an empty if -- and can t work out the logic -- use pass    if some-condition-that s-too-complex-for-me-to-invert       pass  else        do real work here

User · Answer

You can do   if not  u0  lt   u  lt   u0 step       u0   u0  step   change the condition until it is satisfied else      do sth    condition is satisfied   Using a loop   while not  u0  lt   u  lt   u0 step      u0   u0  step   change the condition until it is satisfied do sth    condition is satisfied

User · Answer

There are two ways  In case of doubt  you can always just try it  If it does not work  you can add extra braces to make sure  like that   if not   u0  lt   u  and  u  lt  u0 step

User · Answer

In this particular case the clearest solution is the S Lott answer  But in some complex logical conditions I would prefer use some boolean algebra to get a clear solution    Using De Morgan s law    A B      Av  B  not  u0  lt   u and u  lt  u0 step   not u0  lt   u  or  not u  lt  u0 step  u0  gt  u or u  gt   u0 step   then  if u0  gt  u or u  gt   u0 step      pass       in this case the   clear   solution is not more clear  P

[python] How to use comparison and ' if not' in python?

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