Expression Reference
How to represent the different kinds of Python expressions as Expression Trees
Operations
Boolean Operation - and
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Boolean Operation - or
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Boolean Operation - sequence of and
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The Python AST represents a sequence of boolops as a single node, but to better represent the structure of the code and the grammar of the language, we represent long boolops as composed binary operations
Boolean Operation - mixing and & or
A boolean operations mixing 'and', 'or' in its expression. Operator 'and' has the precedence
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Named Expression/Walrus Operator
An assignment expression, also known as the Walrus Operator, from PEP 572.
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - sum
A binary operation performing the sum between 1 and 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - difference
A binary operation performing the difference between 1 and 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - multiplication
A binary operation performing the multiplication between 1 and 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - division
A binary operation performing the division between 2 and 1
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - floor division
A binary operation performing floor division between 4 and 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - modulo
A binary operation performing 10 modulo 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - exponentiation
A binary operation performing 2 to the power of 10
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: Exponentiation can result in either a float (as in 1.5**2) or an int (as in 2**2 or 2e90**2)
Binary Operation - bitwise shift left
A binary operation performing 1 bit shift to left on number 2
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - bitwise shift right
A binary operation performing 1 bit shift to right on number 4
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - bitwise or
A binary operation performing a bitwise 'or' between 6 and 1
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - bitwise xor
A binary operation performing the bitwise exclusive or between 1 and 1
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - bitwise and
A binary operation performing the bitwise and between 15 and 15
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Binary Operation - 2 consecutive operations
2 consecutive sum binary operation
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Unary Operation - unary positive
A unary plus operation
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Unary Operation - unary negation
A negative unary operation
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Unary Operation - bitwise negation
A bitwise negation
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Lambda
Lambda - one parameter
Lambda, an anonymous function containing only one parameter and one expression
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Lambda - no parameters
Lambda, an anonymous function containing only one expression and no parameters
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Lambda - full parameters kind
A Lambda function containing every single type of possible parameter
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Conditionals
If Expression
If expression with 1 as the result if the condition is True, else 0
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Collections
List - one element
List expression with only one single element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
List - no elements
List expression containing no elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
List - multiple elements
List expression containing multiple elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
List - unpacking
List expression containing multiple elements, including a starred element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The unpacking is represented in the AST as a Starred node, containing the expression to be unpacked, but following the principle that subexpressions should be extractable as an expression in their own right, we chose not to represent the Starred node as a node in the expression tree, as you can't, for example, write an assignment with a Starred node on its right hand side (x = *[1, 2])
Tuple - one element
Tuple expression with only one single element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Tuple - no elements
Tuple expression containing no elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Tuple - multiple elements
Tuple expression containing multiple elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Tuple - unpacking
Tuple expression containing multiple elements, including a Starred element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Dictionary - one element
Dictionary expression with only one single element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Dictionary - no elements
Dictionary expression with no elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Dictionary - unpacking
Dictionary expression with only one keyword argument
Specification
Given the following snippet of code:
From this context, we know that:
- myotherdict is of type Any
The Expression Tree for the highlighted expression is:
Dictionary - multiple arguments
Dictionary expression with multiple arguments and kwargs
Specification
Given the following snippet of code:
From this context, we know that:
- myotherdict2 is of type Any
- myotherdict1 is of type Any
The Expression Tree for the highlighted expression is:
Set - one element
Set expression with only one single element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Set - multiple elements
Set expression containing multiple elements
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Set - unpacking
Set expression containing multiple elements, including a starred element
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Comprehension
List Comprehension - one generator
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
List Comprehension - generators and filters
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Set Comprehension - one generator
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Dictionary Comprehension - one generator
A dictionary comprehension giving for each number in numbers the number as key and its power of 2 as value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Generator Expression - one generator
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Keyword
Await expression
Await expression returning number 404
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Yield expression
Yield expression returning number 404
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Yield From expression
Yield From expression yielding from variable mylist
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
Comparison
Compare - equality
Compare expression using equality operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - difference
Compare expression using difference comparison operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - less than
Compare expression using less than comparison operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - less than or equal to
Compare expression using less than or equal to comparison operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - greater than
Compare expression using greater than comparison operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - greater than or equal to
Compare expression using greater than or equal to comparison operator
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Compare - identity equality operator
Compare expression using the identity equality operator stating if the objects compared are the same
Specification
Given the following snippet of code:
From this context, we know that:
- obj2 is of type Any
- obj1 is of type Any
The Expression Tree for the highlighted expression is:
Compare - identity difference operator
Compare expression using the identity difference operator stating if the objects compared are not the same
Specification
Given the following snippet of code:
From this context, we know that:
- obj2 is of type Any
- obj1 is of type Any
The Expression Tree for the highlighted expression is:
Compare - 'in' membership operator
Compare expression using the 'in' membership operator to test if a sequence is present in an object
Specification
Given the following snippet of code:
From this context, we know that:
- numbers is of type Any
The Expression Tree for the highlighted expression is:
Compare expression using the 'not in' membership operator to test if a sequence is not present in an object
Compare expression
Specification
Given the following snippet of code:
From this context, we know that:
- numbers is of type Any
The Expression Tree for the highlighted expression is:
Functions
Call expression
Function call expression with every possible type of parameter
Specification
Given the following snippet of code:
From this context, we know that:
- j is of type Any
- h is of type Any
- g is of type Any
- f is of type Any
- e is of type Any
- d is of type Any
- c is of type Any
- z is of type Any
- y is of type Any
- x is of type Any
- func is of type Any
- m is of type Any
- l is of type Any
The Expression Tree for the highlighted expression is:
Rationale: Order of parameters it not perfectly preserved in the AST: starargs which are placed after a keyword arg cannot be distinguished from starargs placed immediately before the first keyword arg. Hence starargs after keyword args are reordered to before the keyword args. This is the most common usage pattern and reflects the method definition too.
Constant
Integer constant expression
Constant literal expression of a integer number
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
String constant expression
Constant literal expression of a string
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Concatenated string constant expression
Constant literal expression of a concatenated string
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: Python concatenates adjacent string literals in source code. This concatenation happens while parsing the source code, before compilation and execution, so we represent it as such too.
Concatenated f-string constant expression
Constant literal expression of a concatenated string
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: In violation of PEP 498, which specifies that f-strings should be concatenated at runtime, the parser concatenates f-strings too, though it enforces the requirement that a FormattedValue must be fully contained in a single string and may not cross a concatenated string boundary.
Constant expression
Constant literal expression of a float
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Constant literal expression of a boolean
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Constant literal expression of a NoneType
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Constant literal expression of an ellipsis
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Constant literal expression of an ellipsis
Specification
Given the following snippet of code:
From this context, we know that:
- Ellipsis is of type ellipsis
The Expression Tree for the highlighted expression is:
Attribute
Attribute
An object attribute expression
Specification
Given the following snippet of code:
From this context, we know that:
- snake is of type Any
The Expression Tree for the highlighted expression is:
Subscript
Subscript expression
A subscript expression of a sequence with the zero position being accessed
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
Sliced Subscription
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
A subscript giving a slice of the sequence
Specification
Given the following snippet of code:
From this context, we know that:
- mylist is of type Any
The Expression Tree for the highlighted expression is:
Name
Name expression
Given the following snippet of code:
From this context, we know that:
- myvar is of type Any
The Expression Tree for the highlighted expression is:
f-string
Formatted String - no formatted value
A simple formatted string used without inner formatted values
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Formatted String - single formatted value
A formatted string with an inner formatted value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Formatted String - single formatted value with format string
A formatted string with an inner formatted value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The format string is a JoinedStr contained in the FormattedValue node, and as such could be considered a subexpression, however, it is quite different from other JoinedStrs, so we decided to represent it as part of the FormattedValue. Unlike regular f-strings it is not wrapped in quotes, it can contain only interpolations with a depth of one, and it is different in content as it may not be an arbitrary string but rather follows the format mini-language.
Formatted String - single formatted value with nested format string
A formatted string with an inner formatted value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Formatted String - single formatted value with = formatting
A formatted string with an inner formatted value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The formatting of an =-terminated formatted value is performed while parsing
Formatted String - single formatted value with conversion specifier
A formatted string with an inner formatted value
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Odd Types
Type of tuple
A reference to the `tuple` type/constructor
Specification
Given the following snippet of code:
From this context, we know that:
- tuple is of type Type[Tuple[Any, ...]]
The Expression Tree for the highlighted expression is:
Rationale: The type of types can be somewhat difficult to parse and recursive.
Type of a class name
A reference to a user-defined class
Specification
Given the following snippet of code:
From this context, we know that:
- C is of type Type[C]
The Expression Tree for the highlighted expression is:
Type of a class name - nonglobal
A reference to a user-defined class, declared in a function body
Specification
Given the following snippet of code:
From this context, we know that:
- C is of type Type[Any]
The Expression Tree for the highlighted expression is:
Rationale: For unknown reasons, pytype assigns the wrong type to class definitions not in the global scope.
Type of None
A reference to the None singleton
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: Formally, None has the type NoneType, however, None is accepted as a type hint for variables containing None
The NoReturn type
A function with the NoReturn return type
Specification
Given the following snippet of code:
From this context, we know that:
- NoReturn is of type nothing
The Expression Tree for the highlighted expression is:
Rationale: The NoReturn type is a special type which contains no values and is used to label functions that are not expected to return at all (i.e. they run forever or terminate exceptionally). Pytype, however, incorrectly labels NoReturn with the type nothing.
Type of yield
A yield expression
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The type of an arbitrary yield expression is Any because the value it evaluates to depends on the caller.
A yield expression in a type-hinted function
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: The type of a yield expression in a function that is type hinted to return a Generator is determined by the type hint.
Type of yield from
A yield from expression with a generator
Specification
Given the following snippet of code:
From this context, we know that:
- bar is of type Callable[[], Any]
The Expression Tree for the highlighted expression is:
Rationale: The yield from expression evaluates to the value returned by its iterable.
A yield from expression with a list
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: Yielding from a list evaluates to None, but pytype incorrectly assigns it listiterator instead.
The 'nothing' type
A list containing nothing
Specification
Given the following snippet of code:
The Expression Tree for the highlighted expression is:
Rationale: Pytype uses the 'nothing' type to represent the "empty" type which contains no values. This type is not provided by the standard library, nor indeed by any publicly available package, but made up by pytype, so it cannot be used in type hints except when using pytype.