↑ Python | Python Variables

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Python - Booleans

• True
• False

my_list = [1, 2]
if my_list
# is the same as:
if bool(my_list)

Casting

bool(1) # True
bool(-1) # True
bool(1j) # True

bool(0) # False
bool(0.0) # False
bool(0j) # False

bool('True') # True
bool('False') # True
bool(' ') # True
bool('') # False

bool([1, 2]) # True
bool([]) # False

bool({}) # False

bool(None) # False

Logic

see: Control Flow

nice_weather = False
have_umbrella = True

if not have_umbrella or nice_weather:
# if (not have_umbrella) or nice_weather:
  print('stay inside')
else:
  print('go outside') # executed

The above code prints go outside because not have_umbrella evaluates first (python reads booleans from left to right), and it seems working but if we flip the variables we get:

nice_weather = True
have_umbrella = False

if not have_umbrella or nice_weather:
  print('stay inside') # executed
else:
  print('go outside')

The code now prints stay inside which is wrong since nice_weather = True, to fix it we could do:

nice_weather = True
have_umbrella = False

if not (have_umbrella or nice_weather):
  print('stay inside')
else:
  print('go outside') # executed

or using and:

nice_weather = True
have_umbrella = False

if not have_umbrella and not nice_weather: 
# if (not have_umbrella) and (not nice_weather):
  print('stay inside')
else:
  print('go outside') # executed

but the most readable way would be to flip the statements:

nice_weather = True
have_umbrella = False

if have_umbrella or nice_weather:
  print('go outside') # executed
else:
  print('stay inside')