[Python] I'm getting an IndentationError (or a TabError). How do I fix it?

I have a Python script:

if True:
if False:
print('foo')
print('bar')


However, when I attempt to run my script, Python raises an IndentationError:

File "script.py", line 4
print('bar')
^
IndentationError: unindent does not match any outer indentation level


I kept playing around with my program, and I was able to produce four errors in total:

• IndentationError: unexpected indent
• IndentationError: expected an indented block
• TabError: inconsistent use of tabs and spaces in indentation
• IndentationError: unindent does not match any outer indentation level

What do these errors mean? What am I doing wrong? How can I fix my code?


This is a canonical question intended to cover ordinary causes of IndentationError in the same place, because the conceptual problem — knowing how to indent and why/where — is the same.

There are a few established questions for certain more specific cases, where the conceptual problem isn't about the indentation per se:

• 
  How can I write an empty indented block in Python? for cases where everything is lined up as it should be, except that there was a deliberately empty indented block detected as wrong indentation elsewhere.
  
  
• 
  Why do I get an IndentationError from a properly indented function (following a "try" with no "except")? for cases caused by a missing except or finally block. Note that recent versions of Python report the error more clearly, but older ones misleadingly detect the problem as incorrect indentation of the subsequent code.
  
  
• 
  Copy-paste into Python interactive interpreter and indentation is not really about getting the indentation right, but about what happens when pasting code into Python's REPL (because it's expecting a single block at a time, manually typed in). However, this commonly results in an IndentationError being reported.
  

It's also possible to have logically incorrect indentation that does not cause an error. One common form of this is attaching else: to a for or while loop rather than (as intended) the corresponding if:. See Else clause on Python while statement

See How to fix Python indentation for more tools and techniques to clean up indentation to conform to standards (even if it already "works"). Keep in mind that tools cannot automatically fix errors for you; they can only help with editing, or apply cosmetic changes that don't affect the meaning.

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