Static Graph Syntax Support

Linux Ascend GPU CPU Model Development Beginner Intermediate Expert

Overview

In graph mode, Python code is not executed by the Python interpreter. Instead, the code is compiled into a static computation graph, and then the static computation graph is executed.

Currently, only the function, Cell, and subclass instances modified by the @ms_function decorator can be built. For a function, build the function definition. For the network, build the construct method and other methods or functions called by the construct method.

For details about how to use ms_function, click https://www.mindspore.cn/docs/api/en/r1.3/api_python/mindspore.html#mindspore.ms_function.

For details about the definition of Cell, click https://www.mindspore.cn/docs/programming_guide/en/r1.3/cell.html.

Due to syntax parsing restrictions, the supported data types, syntax, and related operations during graph building are not completely consistent with the Python syntax. As a result, some usage is restricted.

The following describes the data types, syntax, and related operations supported during static graph building. These rules apply only to graph mode.

All the following examples run on the network in graph mode. For brevity, the network definition is not described.

The Tensor cannot be directly constructed in static graphs. It can be transferred to the network through parameters or constructed in the __init__ method as a network attribute and then used in the construct method of the network.

Data Types

Built-in Python Data Types

Currently, the following built-in Python data types are supported: Number, String, List, Tuple, and Dictionary.

Number

Supports int, float, and bool, but does not support complex numbers.

Number can be defined on the network. That is, the syntax y = 1, y = 1.2, and y = True are supported.

Forcible conversion to Number is not supported on the network. That is, the syntax y = int(x), y = float(x), and y = bool(x) are not supported.

String

String can be constructed on the network. That is, the syntax y = "abcd" is supported.

Forcible conversion to String is not supported on the network. That is, the syntax y = str(x) is not supported.

List

List can be constructed on the network, that is, the syntax y = [1, 2, 3] is supported.

Forcible conversion to List is not supported on the network. That is, the syntax y = list(x) is not supported.

List to be output in the computation graph will be converted into Tuple.

Supported APIs

append: adds an element to list.

For example:
```
x = [1, 2, 3]
x.append(4)
```
The result is as follows:
```
x: (1, 2, 3, 4)
```

Supported index values and value assignment

Single-level and multi-level index values and value assignment are supported.

The index value supports only int.

The assigned value can be Number, String, Tuple, List, or Tensor.

For example:

x = [[1, 2], 2, 3, 4]

m = x[0][1]
x[1] = Tensor(np.array([1, 2, 3]))
x[2] = "ok"
x[3] = (1, 2, 3)
x[0][1] = 88
n = x[-3]

The result is as follows:

m: 2
x: ([1, 88], Tensor(shape=[3], dtype=Int64, value=[1, 2, 3]), 'ok', (1, 2, 3))
n: Tensor(shape=[3], dtype=Int64, value=[1, 2, 3])

Tuple

Tuple can be constructed on the network, that is, the syntax y = (1, 2, 3) is supported.

Forcible conversion to Tuple is not supported on the network. That is, the syntax y = tuple(x) is not supported.

Supported index values

The index value can be int, slice, Tensor, and multi-level index value. That is, the syntax data = tuple_x[index0][index1]... is supported.

Restrictions on the index value Tensor are as follows:
- Tuple stores Cell. Each Cell must be defined before a tuple is defined. The number of input parameters, input parameter type, and input parameter shape of each Cell must be the same. The number of outputs of each Cell must be the same. The output type must be the same as the output shape.
- The index Tensor is a scalar Tensor whose dtype is int32. The value range is [-tuple_len, tuple_len), negative index is not supported in Ascend backend.
- This syntax does not support the running branches whose control flow conditions if, while, and for are variables. The control flow conditions can be constants only.
- GPU and Ascend backend is supported.
An example of the int and slice indexes is as follows:
```
x = (1, (2, 3, 4), 3, 4, Tensor(np.array([1, 2, 3])))
y = x[1][1]
z = x[4]
m = x[1:4]
n = x[-4]
```
The result is as follows:
```
y: 3
z: Tensor(shape=[3], dtype=Int64, value=[1, 2, 3])
m: ((2, 3, 4), 3, 4)
n: (2, 3, 4)
```
An example of the Tensor index is as follows:
```
class Net(nn.Cell):
    def __init__(self):
        super(Net, self).__init__()
        self.relu = nn.ReLU()
        self.softmax = nn.Softmax()
        self.layers = (self.relu, self.softmax)

    def construct(self, x, index):
        ret = self.layers[index](x)
        return ret
```

Dictionary

Dictionary can be constructed on the network. That is, the syntax y = {"a": 1, "b": 2} is supported. Currently, only String can be used as the key value.

Dictionary to be output in the computational graph will extract all value values to form the Tuple output.

Supported APIs

keys: extracts all key values from dict to form Tuple and return it.

values: extracts all value values from dict to form Tuple and return it.

For example:

x = {"a": Tensor(np.array([1, 2, 3])), "b": Tensor(np.array([4, 5, 6])), "c": Tensor(np.array([7, 8, 9]))}
y = x.keys()
z = x.values()

The result is as follows:

y: ("a", "b", "c")
z: (Tensor(shape=[3], dtype=Int64, value=[1, 2, 3]), Tensor(shape=[3], dtype=Int64, value=[4, 5, 6]), Tensor(shape=[3], dtype=Int64, value=[7, 8, 9]))

Supported index values and value assignment

The index value supports only String. The assigned value can be Number, Tuple, or Tensor.

For example:

x = {"a": Tensor(np.array([1, 2, 3])), "b": Tensor(np.array([4, 5, 6])), "c": Tensor(np.array([7, 8, 9]))}
y = x["b"]
x["a"] = (2, 3, 4)

The result is as follows:

y: Tensor(shape=[3], dtype=Int64, value=[4, 5, 6])
x: {"a": (2, 3, 4), Tensor(shape=[3], dtype=Int64, value=[4, 5, 6]), Tensor(shape=[3], dtype=Int64, value=[7, 8, 9])}

MindSpore User-defined Data Types

Currently, MindSpore supports the following user-defined data types: Tensor, Primitive, and Cell.

Tensor

Currently, tensors cannot be constructed on the network. That is, the syntax x = Tensor(args...) is not supported.

You can use the @constexpr decorator to modify the function and generate the Tensor in the function.

For details about how to use @constexpr, click https://www.mindspore.cn/docs/api/en/r1.3/api_python/ops/mindspore.ops.constexpr.html.

The constant Tensor used on the network can be used as a network attribute and defined in init, that is, self.x = Tensor(args...). Then the constant can be used in construct.

In the following example, Tensor of shape = (3, 4), dtype = int64 is generated by @constexpr.

@constexpr
def generate_tensor():
    return Tensor(np.ones((3, 4)))

The following describes the attributes, APIs supported by the Tensor.

Supported attributes

shape: obtains the shape of Tensor and returns a Tuple.

dtype: obtains the data type of Tensor and returns a data type defined by MindSpore.
Supported APIs

all: reduces Tensor through the all operation. Only Tensor of the Bool type is supported.

any: reduces Tensor through the any operation. Only Tensor of the Bool type is supported.

view: reshapes Tensor into input shape.

expand_as: expands Tensor to the same shape as another Tensor based on the broadcast rule.

For example:

x = Tensor(np.array([[True, False, True], [False, True, False]]))
x_shape = x.shape
x_dtype = x.dtype
x_all = x.all()
x_any = x.any()
x_view = x.view((1, 6))

y = Tensor(np.ones((2, 3), np.float32))
z = Tensor(np.ones((2, 2, 3)))
y_as_z = y.expand_as(z)

The result is as follows:

x_shape: (2, 3)
x_dtype: Bool
x_all: Tensor(shape=[], dtype=Bool, value=False)
x_any: Tensor(shape=[], dtype=Bool, value=True)
x_view: Tensor(shape=[1, 6], dtype=Bool, value=[[True, False, True, False, True, False]])

y_as_z: Tensor(shape=[2, 2, 3], dtype=Float32, value=[[[1.0, 1.0, 1.0], [1.0, 1.0, 1.0]], [[1.0, 1.0, 1.0], [1.0, 1.0, 1.0]]])

Primitive

Currently, Primitive and its subclass instances can be constructed on the network. That is, the reduce_sum = ReduceSum(True) syntax is supported.

However, during construction, the parameter can be specified only in position parameter mode, and cannot be specified in the key-value pair mode. That is, the syntax reduce_sum = ReduceSum(keep_dims=True) is not supported.

Currently, the attributes and APIs related to Primitive and its subclasses cannot be called on the network.

For details about the definition of Primitive, click https://www.mindspore.cn/docs/programming_guide/en/r1.3/operators.html.

For details about the defined Primitive, click https://www.mindspore.cn/docs/api/en/r1.3/api_python/mindspore.ops.html.

Cell

Currently, Cell and its subclass instances can be constructed on the network. That is, the syntax cell = Cell(args...) is supported.

However, during construction, the parameter can be specified only in position parameter mode, and cannot be specified in the key-value pair mode. That is, the syntax cell = Cell(arg_name=value) is not supported.

Currently, the attributes and APIs related to Cell and its subclasses cannot be called on the network unless they are called through self in contrcut of Cell.

For details about the definition of Cell, click https://www.mindspore.cn/docs/programming_guide/en/r1.3/cell.html.

For details about the defined Cell, click https://www.mindspore.cn/docs/api/en/r1.3/api_python/mindspore.nn.html.

Operators

Arithmetic operators and assignment operators support the Number and Tensor operations, as well as the Tensor operations of different dtype.

This is because these operators are converted to operators with the same name for computation, and they support implicit type conversion.

For details about the rules, click https://www.mindspore.cn/docs/note/en/r1.3/operator_list_implicit.html.

Arithmetic Operators

Arithmetic Operator	Supported Type
`+`	`Number` + `Number`, `Tensor` + `Tensor`, `Tensor` + `Number`, `Tuple` + `Tuple`, `String` + `String`, and `List` + `List`
`-`	`Number` - `Number`, `Tensor` - `Tensor`, and `Tensor` - `Number`
`*`	`Number` * `Number`, `Tensor` * `Tensor`, and `Tensor` * `Number`
`/`	`Number` / `Number`, `Tensor` / `Tensor`, and `Tensor` / `Number`
`%`	`Number` % `Number`, `Tensor` % `Tensor`, and `Tensor`% `Number`
`**`	`Number` `Number`, `Tensor` `Tensor`, and `Tensor` ** `Number`
`//`	`Number` // `Number`, `Tensor` // `Tensor`, and `Tensor` // `Number`
`~`	`~Tensor[Bool]`

Assignment Operators

Assignment Operator	Supported Type
`=`	Scalar and `Tensor`
`+=`	`Number` += `Number`, `Tensor` += `Tensor`, `Tensor` += `Number`, `Tuple` += `Tuple`, and `String` += `String`
`-=`	`Number` -= `Number`, `Tensor` -= `Tensor`, and `Tensor` -= `Number`
`*=`	`Number` = `Number`, `Tensor` = `Tensor`, and `Tensor` *= `Number`
`/=`	`Number` /= `Number`, `Tensor` /= `Tensor`, and `Tensor` /= `Number`
`%=`	`Number` %= `Number`, `Tensor` %= `Tensor`, and `Tensor` %= `Number`
`**=`	`Number` = `Number`, `Tensor` = `Tensor`, and `Tensor` **= `Number`
`//=`	`Number` //= `Number`, `Tensor` //= `Tensor`, and `Tensor` //= `Number`

Logical Operators

Logical Operator	Supported Type
`and`	`Number` and `Number`, `Tensor`, and `Tensor`
`or`	`Number` or `Number`, and `Tensor` or `Tensor`
`not`	not `Number`, not `Tensor`, and not `tuple`

Member Operators

Member Operator	Supported Type
`in`	`Number` in `tuple`, `String` in `tuple`, `Tensor` in `Tuple`, `Number` in `List`, `String` in `List`, `Tensor` in `List`, and `String` in `Dictionary`
`not in`	Same as `in`

Identity Operators

Identity Operator	Supported Type
`is`	The value can only be `None`, `True`, or `False`.
`is not`	The value can only be `None`, `True`, or `False`.

Expressions

Conditional Control Statements

single if

Usage:

if (cond): statements...
x = y if (cond) else z

Parameter: cond – The supported types are Number, Tuple, List, String, None, Tensor and Function. It can also be an expression whose computation result type is one of them.

Restrictions:

During graph building, if if is not eliminated, the data type and shape of return inside the if branch must be the same as those outside the if branch.
When only if is available, the data type and shape of the if branch variable after the update must be the same as those before the update.
When both if and else are available, the updated data type and shape of the if branch variable must be the same as those of the else branch.
Does not support higher-order differential.
Does not support elif statements.

Example 1:

if x > y:
  return m
else:
  return n

The data types of m returned by the if branch and n returned by the else branch must be the same as those of shape.

Example 2:

if x > y:
  out = m
else:
  out = n
return out

The data types of out after the if branch is updated and else after the out branch is updated must be the same as those of shape.

side-by-side if

Usage:

if (cond1):statements else:statements...if (cond2):statements...

Parameters: cond1 and cond2 – Consistent with single if.

Restrictions:

Inherit all restrictions of single if.
The total number of if in calculating graph can not exceed 50.
Too many if will cause the compilation time to be too long. Reducing the number of if will help improve compilation efficiency.

Example:

if x > y:
  out = x
else:
  out = y
if z > x:
  out = out + 1
return out

if in if

Usage:

if (cond1):if (cond2):statements...

Parameters: cond1 and cond2 – Consistent with single if.

Restrictions:

Inherit all restrictions of single if.
The total number of if in calculating graph can not exceed 50.
Too many if will cause the compilation time to be too long. Reducing the number of if will help improve compilation efficiency.

Example:

if x > y:
  z = z + 1
  if z > x:
    return m
else:
  return n

Loop Statements

for

Usage:

for i in sequence

Parameter: sequence –Iterative sequences (Tuple and List).

Restrictions:

The total number of graph operations is a multiple of number of iterations of the for loop. Excessive number of iterations of the for loop may cause the graph to occupy more memory than usage limit.

Example:

z = Tensor(np.ones((2, 3)))
x = (1, 2, 3)
for i in x:
  z += i
return z

The result is as follows:

z: Tensor(shape=[2, 3], dtype=Int64, value=[[7, 7], [7, 7], [7, 7]])

single while

Usage:

while (cond)

Parameter: cond – Consistent with single if.

Restrictions:

During graph building, if while is not eliminated, the data type and shape of return inside while must be the same as those outside while.
The data type and shape of the updated variables in while must be the same as those before the update.
Does not support training scenarios.

Example 1:

while x < y:
  x += 1
  return m
return n

The m data type returned inside while inside and n data type returned outside while must be the same as those of shape.

Example 2:

out = m
while x < y:
  x += 1
  out = out + 1
return out

In while, the data types of out before and after update must be the same as those of shape.

side-by-side while

Usage:

while (cond1):statements while (cond2):statemetns...

Parameters: cond1 and cond2 – Consistent with single if.

Restrictions:

Inherit all restrictions of single while.
The total number of while in calculating graph can not exceed 50.
Too many while will cause the compilation time to be too long. Reducing the number of while will help improve compilation efficiency.

Example:

out = m
while x < y:
  x += 1
  out = out + 1
while out > 10:
  out -= 10
return out

while in while

Usage:

-while (cond1):while (cond2):statements...

Parameters: cond1 and cond2 – Consistent with single if.

Restrictions:

Inherit all restrictions of single while.
The total number of while in calculating graph can not exceed 50.
Too many while will cause the compilation time to be too long. Reducing the number of while will help improve compilation efficiency.

Example:

out = m
while x < y:
  while z < y:
    z += 1
    out = out + 1
  x += 1
return out

Conditional Control Statements in Loop Statements

if in for

Usage:

for i in sequence:if (cond)`

Parameters:

cond – Consistent with single if.
sequence – Iterative sequence(Tuple、List)

Restrictions:

Inherit all restrictions of single if.
Inherit all restrictions of for.
If cond is variable, it is forbidden to use if (cond):return,if (cond):continue,if (cond):break statements.
The total number of if is a multiple of number of iterations of the for loop. Excessive number of iterations of the for loop may cause the compilation time to be too long.

Example:

z = Tensor(np.ones((2, 3)))
x = (1, 2, 3)
for i in x:
  if i < 3:
    z += i
return z

The result is as follows:

z: Tensor(shape=[2, 3], dtype=Int64, value=[[4, 4], [4, 4], [4, 4]])

if in while

Usage:

while (cond1):if (cond2)

Parameters: cond1 and cond2 – Consistent with single if.

Restrictions:

Inherit all restrictions of single if and single while.
If cond2 is variable, it is forbidden to use if (cond2):return,if (cond2):continue,if (cond2):break statements.

Example:

out = m
while x < y:
  if z > 2*x:
    out = out + 1
  x += 1
return out

Function Definition Statements

def Keyword

Defines functions.

Usage:

def function_name(args): statements...

For example:

def number_add(x, y):
  return x + y
ret = number_add(1, 2)

The result is as follows:

ret: 3

lambda Expression

Generates functions.

Usage: lambda x, y: x + y

For example:

number_add = lambda x, y: x + y
ret = number_add(2, 3)

The result is as follows:

ret: 5

Functions

Python Built-in Functions

Currently, the following built-in Python functions are supported: len, isinstance, partial, map, range, enumerate, super, and pow.

len

Returns the length of a sequence.

Calling: len(sequence)

Input parameter: sequence – Tuple, List, Dictionary, or Tensor.

Return value: length of the sequence, which is of the int type. If the input parameter is Tensor, the length of dimension 0 is returned.

For example:

x = (2, 3, 4)
y = [2, 3, 4]
d = {"a": 2, "b": 3}
z = Tensor(np.ones((6, 4, 5)))
x_len = len(x)
y_len = len(y)
d_len = len(d)
z_len = len(z)

The result is as follows:

x_len: 3
y_len: 3
d_len: 2
z_len: 6

isinstance

Determines whether an object is an instance of a class. Different from operator Isinstance, the second input parameter of Isinstance is the type defined in the dtype module of MindSpore.

Calling: isinstance(obj, type)

Input parameters:

obj – Any instance of any supported type.
type – A type in the MindSpore dtype module.

Return value: If obj is an instance of type, return True. Otherwise, return False.

For example:

x = (2, 3, 4)
y = [2, 3, 4]
z = Tensor(np.ones((6, 4, 5)))
x_is_tuple = isinstance(x, mstype.tuple_)
y_is_list= isinstance(y, mstype.list_)
z_is_tensor = isinstance(z, mstype.tensor)

The result is as follows:

x_is_tuple: True
y_is_list: True
z_is_tensor: True

partial

A partial function used to fix the input parameter of the function.

Calling: partial(func, arg, ...)

Input parameters:

func –Function.
arg – One or more parameters to be fixed. Position parameters and key-value pairs can be specified.

Return value: functions with certain input parameter values fixed

For example:

def add(x, y):
  return x + y

add_ = partial(add, x=2)
m = add_(y=3)
n = add_(y=5)

The result is as follows:

m: 5
n: 7

map

Maps one or more sequences based on the provided functions and generates a new sequence based on the mapping result. If the number of elements in multiple sequences is inconsistent, the length of the new sequence is the same as that of the shortest sequence.

Calling: map(func, sequence, ...)

Input parameters:

func –Function.
sequence – One or more sequences (Tuple or List).

Return value: A Tuple

For example:

def add(x, y):
  return x + y

elements_a = (1, 2, 3)
elements_b = (4, 5, 6)
ret = map(add, elements_a, elements_b)

The result is as follows:

ret: (5, 7, 9)

zip

Packs elements in the corresponding positions in multiple sequences into tuples, and then uses these tuples to form a new sequence. If the number of elements in each sequence is inconsistent, the length of the new sequence is the same as that of the shortest sequence.

Calling: zip(sequence, ...)

Input parameter: sequence – One or more sequences (Tuple or List)`.

Return value: A Tuple

For example:

elements_a = (1, 2, 3)
elements_b = (4, 5, 6)
ret = zip(elements_a, elements_b)

The result is as follows:

ret: ((1, 4), (2, 5), (3, 6))

range

Creates a Tuple based on the start value, end value, and step.

Calling:

range(start, stop, step)
range(start, stop)
range(stop)

Input parameters:

start – start value of the count. The type is int. The default value is 0.
stop – end value of the count (exclusive). The type is int.
step – Step. The type is int. The default value is 1.

Return value: A Tuple

For example:

x = range(0, 6, 2)
y = range(0, 5)
z = range(3)

The result is as follows:

x: (0, 2, 4)
y: (0, 1, 2, 3, 4)
z: (0, 1, 2)

enumerate

Generates an index sequence of a sequence. The index sequence contains data and the corresponding subscript.

Calling:

enumerate(sequence, start)
enumerate(sequence)

Input parameters:

sequence – A sequence (Tuple, List, or Tensor).
start – Start position of the subscript. The type is int. The default value is 0.

Return value: A Tuple

For example:

x = (100, 200, 300, 400)
y = Tensor(np.array([[1, 2], [3, 4], [5 ,6]]))
m = enumerate(x, 3)
n = enumerate(y)

The result is as follows:

m: ((3, 100), (4, 200), (5, 300), (5, 400))
n: ((0, Tensor(shape=[2], dtype=Int64, value=[1, 2])), (1, Tensor(shape=[2], dtype=Int64, value=[3, 4])), (2, Tensor(shape=[2], dtype=Int64, value=[5, 6])))

super

Calls a method of the parent class (super class). Generally, the method of the parent class is called after super.

Calling:

super().xxx()
super(type, self).xxx()

Input parameters:

type –Class.
self –Object.

Return value: method of the parent class.

For example:

class FatherNet(nn.Cell):
  def __init__(self, x):
      super(FatherNet, self).__init__(x)
      self.x = x

  def construct(self, x, y):
      return self.x * x

  def test_father(self, x):
      return self.x + x

class SingleSubNet(FatherNet):
def __init__(self, x, z):
    super(SingleSubNet, self).__init__(x)
    self.z = z

def construct(self, x, y):
    ret_father_construct = super().construct(x, y)
    ret_father_test = super(SingleSubNet, self).test_father(x)
    return ret_father_construct, ret_father_test

pow

Returns the power.

Calling: pow(x, y)

Input parameters:

x – Base number, Number, or Tensor.
y – Power exponent, Number, or Tensor.

Return value: y power of x, Number, or Tensor

For example:

x = Tensor(np.array([1, 2, 3]))
y = Tensor(np.array([1, 2, 3]))
ret = pow(x, y)

The result is as follows:

ret: Tensor(shape=[3], dtype=Int64, value=[1, 4, 27]))

print

Prints logs.

Calling: print(arg, ...)

Input parameter: arg – Information to be printed (int, float, bool, String or Tensor). When the arg is int, float, or bool, it will be printed out as a 0-D tensor.

Return value: none

For example:

x = Tensor(np.array([1, 2, 3]))
y = 3
print("x: ", x)
print("y: ", y)

The result is as follows:

x: Tensor(shape=[3], dtype=Int64, value=[1, 2, 3]))
y: Tensor(shape=[], dtype=Int64, value=3))

Function Parameters

Default parameter value: The data types int, float, bool, None, str, tuple, list, and dict are supported, whereas Tensor is not supported.
Variable parameters: Inference and training of networks with variable parameters are supported.
Key-value pair parameter: Functions with key-value pair parameters cannot be used for backward propagation on computational graphs.
Variable key-value pair parameter: Functions with variable key-value pairs cannot be used for backward propagation on computational graphs.

Network Definition

Instance Types on the Entire Network

Common Python function with the @ms_function decorator.
Cell subclass inherited from nn.Cell.

Network Construction Components

Category	Content
`Cell` instance	mindspore/nn/* and user-defined Cell.
Member function of a `Cell` instance	Member functions of other classes in the construct function of Cell can be called.
`dataclass` instance	Class decorated with @dataclass.
`Primitive` operator	mindspore/ops/operations/*
`Composite` operator	mindspore/ops/composite/*
`constexpr` generation operator	Value computation operator generated by @constexpr.
Function	User-defined Python functions and system functions listed in the preceding content.

Network Constraints

By default, the input parameters of the entire network (that is, the outermost network input parameters) support only Tensor. To support non-Tensor, you can set the support_non_tensor_inputs attribute of the network to True.

During network initialization, self.support_non_tensor_inputs = True is set. Currently, this configuration supports only the forward network and does not support the backward network. That is, the backward operation cannot be performed on the network whose input parameters are not Tensor.

The following is an example of supporting the outermost layer to transfer scalars:
```
class ExpandDimsNet(nn.Cell):
    def __init__(self):
        super(ExpandDimsNet, self).__init__()
        self.support_non_tensor_inputs = True
        self.expandDims = ops.ExpandDims()

    def construct(self, input_x, input_axis):
        return self.expandDims(input_x, input_axis)
expand_dim_net = ExpandDimsNet()
input_x = Tensor(np.random.randn(2,2,2,2).astype(np.float32))
expand_dim_net(input_x, 0)
```

You are not allowed to modify non-Parameter data members of the network.

For example:

class Net(Cell):
    def __init__(self):
        super(Net, self).__init__()
        self.num = 2
        self.par = Parameter(Tensor(np.ones((2, 3, 4))), name="par")

    def construct(self, x, y):
        return x + y

In the preceding defined network, self.num is not a Parameter and cannot be modified. self.par is a Parameter and can be modified.

When an undefined class member is used in the construct function, AttributeError is not thrown like the Python interpreter. Instead, it is processed as None.

For example:
```
class Net(Cell):
    def __init__(self):
        super(Net, self).__init__()

    def construct(self, x):
        return x + self.y
```
In the preceding defined network, construct uses the undefined class member self.y. In this case, self.y is processed as None.