What does the “|” sign mean in Python?

Question

This question originally asked (wrongly) what does "|" mean in Python, when the actual question was about Django. That question had a wonderful answer by Triptych I want to preserve.

Countrywide

Nice try, but when you make the post CW, all the responses are CW as well. – Interlocutory

The community wiki checkbox is marked by default, you can deselect it to have a non community wiki answer – Countrywide

This just shouldn't be a CW post. It's not a "real" question because Vinko probably already knows the answer. But it's still real in that it's about programming and people can google for it and such. – Chiquita

Yes, that's why I didn't want to let your answer go to waste – Countrywide

Thanks. I was a little annoyed, honestly, that a decent answer would go to waste because a question was improperly phrased. Interesting, the sort of problems that crop up as we trailblaze the wiki Q&A space. – Chiquita

possible duplicate of Pipe character in Python – Fungal

@Pureferret: this is a more general question than the other, which is only about us as bitwise OR operator. – Buttaro

Answer 1

In Python, the '|' operator is defined by default on integer types and set types.

If the two operands are integers, then it will perform a bitwise or, which is a mathematical operation.

If the two operands are set types, the '|' operator will return the union of two sets.

a = set([1,2,3])
b = set([2,3,4])
c = a|b  # = set([1,2,3,4])

Additionally, authors may define operator behavior for custom types, so if something.property is a user-defined object, you should check that class definition for an __or__() method, which will then define the behavior in your code sample.

So, it's impossible to give you a precise answer without knowing the data types for the two operands, but usually it will be a bitwise or.

Chiquita

Answer 2

Bitwise OR

Impanation

Answer 3

In Python, the | symbol is used as a bitwise OR operator for integers and a union operator for sets and some other data structures.

Bitwise OR for Integers

When used between two integers, | performs a bitwise OR operation. This means it compares each bit of the integers and returns a new integer where each bit is set to 1 if at least one of the corresponding bits of the original integers is 1. Here's an example:

a = 5    # Binary: 0101
b = 3    # Binary: 0011

result = a | b  # Binary: 0111, which is 7 in decimal
print(result)  # Output: 7

Union for Sets

When used between two sets, | returns a new set that is the union of the two sets. The union of two sets is a set containing all the elements that are in either set. Here's an example:

set1 = {1, 2, 3}
set2 = {3, 4, 5}

result = set1 | set2  # {1, 2, 3, 4, 5}
print(result)  # Output: {1, 2, 3, 4, 5}

Other Data Structures

The | operator can also be used with other data structures that support the union operation, such as dictionaries (in Python 3.9+), to merge their keys.

dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

result = dict1 | dict2  # {'a': 1, 'b': 3, 'c': 4}
print(result)  # Output: {'a': 1, 'b': 3, 'c': 4}

In this case, the union operation combines the keys of both dictionaries, with values from the second dictionary overwriting those from the first in case of key collisions.

In Some cases, | is used for creating pipeline structure(similar concept of pipeline in linux). Just like in apache-beam: Running pipeline in apache-beam

@beam.ptransform_fn
def CountWords(pcoll):
  return (
      pcoll
      # Convert lines of text into individual words.
      | 'ExtractWords' >>
      beam.FlatMap(lambda x: re.findall(r'[A-Za-z\']+', x))

      # Count the number of times each word occurs.
      | beam.combiners.Count.PerElement())

counts = lines | CountWords()

Piano

Answer 4

New In Python 3.9 - dict also supports the | operator

Full details in PEP 584

Demo:

a: dict = {"arms": 2}
b: dict = {"legs": 2}
c = a | b
print(c)

Prints:

{'arms': 2, 'legs': 2}

Greasy

Answer 5

It could also be "tricked" into a pipe like in unix shells, see here http://code.google.com/p/python-pipeline/

Scleritis