eval(expr: 'str | BinOp', parser: 'str' = 'pandas', engine: 'str | None' = None, truediv=<no_default>, local_dict=None, global_dict=None, resolvers=(), level=0, target=None, inplace=False)
The following arithmetic operations are supported: +
, -
, *
, /
, **
, %
, //
(python engine only) along with the following boolean operations: |
(or), &
(and), and ~
(not). Additionally, the 'pandas'
parser allows the use of and
, or
, and not
with the same semantics as the corresponding bitwise operators. ~pandas.Series
and ~pandas.DataFrame
objects are supported and behave as they would with plain ol' Python evaluation.
The dtype
of any objects involved in an arithmetic %
operation are recursively cast to float64
.
See the enhancing performance <enhancingperf.eval>
documentation for more details.
The expression to evaluate. This string cannot contain any Python :None:None:`statements
<https://docs.python.org/3/reference/simple_stmts.html#simple-statements>`
, only Python :None:None:`expressions
<https://docs.python.org/3/reference/simple_stmts.html#expression-statements>`
.
The parser to use to construct the syntax tree from the expression. The default of 'pandas'
parses code slightly different than standard Python. Alternatively, you can parse an expression using the 'python'
parser to retain strict Python semantics. See the enhancing performance <enhancingperf.eval>
documentation for more details.
The engine used to evaluate the expression. Supported engines are
None
None
'python'
: Performs operations as if you had eval
'd in top
level python. This engine is generally not that useful.
More backends may be available in the future.
Whether to use true division, like in Python >= 3.
A dictionary of local variables, taken from locals() by default.
A dictionary of global variables, taken from globals() by default.
A list of objects implementing the __getitem__
special method that you can use to inject an additional collection of namespaces to use for variable lookup. For example, this is used in the ~DataFrame.query
method to inject the DataFrame.index
and DataFrame.columns
variables that refer to their respective ~pandas.DataFrame
instance attributes.
The number of prior stack frames to traverse and add to the current scope. Most users will not need to change this parameter.
This is the target object for assignment. It is used when there is variable assignment in the expression. If so, then :None:None:`target`
must support item assignment with string keys, and if a copy is being returned, it must also support .copy()
.
If :None:None:`target`
is provided, and the expression mutates :None:None:`target`
, whether to modify :None:None:`target`
inplace. Otherwise, return a copy of :None:None:`target`
with the mutation.
There are many instances where such an error can be raised:
:None:None:`target=None`
, but the expression is multiline.
The expression is multiline, but not all them have item assignment. An example of such an arrangement is this:
a = b + 1 a + 2
Here, there are expressions on different lines, making it multiline, but the last line has no variable assigned to the output of :None:None:`a + 2`
.
:None:None:`inplace=True`
, but the expression is missing item assignment.
Item assignment is provided, but the :None:None:`target`
does not support string item assignment.
Item assignment is provided and :None:None:`inplace=False`
, but the :None:None:`target`
does not support the .copy()
method
The completion value of evaluating the given code or None if inplace=True
.
Evaluate a Python expression as a string using various backends.
DataFrame.eval
Evaluate a string describing operations on DataFrame columns.
DataFrame.query
Evaluates a boolean expression to query the columns of a frame.
>>> df = pd.DataFrame({"animal": ["dog", "pig"], "age": [10, 20]})
... df animal age 0 dog 10 1 pig 20
We can add a new column using pd.eval
:
>>> pd.eval("double_age = df.age * 2", target=df) animal age double_age 0 dog 10 20 1 pig 20 40See :
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