Why is this an issue?

Nested code - blocks of code inside blocks of code - is eventually necessary, but increases complexity. This is why keeping the code as flat as possible, by avoiding unnecessary nesting, is considered a good practice.

Merging if statements when possible will decrease the nesting of the code and improve its readability.

Code like

if condition1:
    if condition2:             # Noncompliant
        # ...

Will be more readable as

if condition1 and condition2:  # Compliant
    # ...

How to fix it

If merging the conditions seems to result in a more complex code, extracting the condition or part of it in a named function or variable is a better approach to fix readability.

Code examples

Noncompliant code example

if file.isValid():
  if file.isfile() or file.isdir():     # Noncompliant
    # ...

Compliant solution

def isFileOrDirectory(File file):
  return file.isFile() or file.isDirectory()

if file.isValid() and isFileOrDirectory(file): # Compliant
  # ...