Python pass StatementThis Python example page explains the use of the pass statement to indicate empty functions, classes and loops.
Pass. Time passes. And often nothing happens. In Python we use the "pass" keyword (a statement) to indicate that nothing happens—the function, class or loop is empty.
With pass, we indicate a "null" block. Pass can be placed on the same line, or on a separate line. Pass can be used to quickly add things that are unimplemented.
Here we use the "pass" statement on two methods. These methods do nothing. But they can be called in Python code.
Result: Nothing happens when the pass methods are called. Pass can be used in other places in Python programs.
Python program that uses pass
# This function does nothing.
# ... It is empty.
def test(n): pass
# Pass can be on a separate line.
# Call our empty functions.
# We are done.
Class example. Sometimes we use the "pass" statement in a class. When we first add a class, we might not be ready to add its entire contents. Pass is helpful.
Python program that uses class with pass
# An empty class.
class Box: pass
# A class with an empty method.
# Create empty class.
x = Box()
# Create class and call empty method.
b = Bird()
# Program is done.
Here we use pass in an if-statement. If a method has a side effect, we sometimes might want to call it even if we do not do anything afterwards.
And: With pass we can add "elif" clauses afterwards. This sometimes makes code clearer to read.
Python program that uses if, pass
# This method has a side effect.
# ... It prints a word.
def equals(name, value):
return name == value
name = "snake"
# Use if-statement with a method that has a side effect.
# ... Use pass to ignore contents of block.
if equals(name, "snake"):
While example. With a while-loop, we can use a "pass" statement. Sometimes we want to keep calling a method while a condition is true. With pass we can use an empty loop body.
Python program that uses while, pass
# Print and return a random int.
result = random.randint(0, 5)
# Continue calling x while its value is at least 1.
# ... Use no loop body.
while x() >= 1:
With pass, we have a null operation. It does nothing—it passes on taking an action. In some languages we might use a semicolon to indicate nothing.
Quote: Pass is a null operation—when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed.Simple statements: python.org
A summary. Python has a full-featured group of keywords. But it has no semicolons. So we must indicate an empty line with a special keyword. That is "pass."
© 2007-2019 Sam Allen. Every person is special and unique. Send bug reports to firstname.lastname@example.org.