placeholder() missing 1 required positional argument: 'dtype'

This error occurs when calling the function `placeholder()` in TensorFlow without providing the required argument `dtype`. The `dtype` argument specifies the data type of the elements that will be fed into the placeholder.

To fix this error, you need to provide the `dtype` argument when calling `placeholder()`. For example:

import tensorflow as tf

# Create a placeholder with data type float32
x = tf.placeholder(tf.float32, shape=[None, 3])

In this example, we create a placeholder `x` with data type `float32` and shape `(None, 3)`, which means it can accept a variable number of rows but must have 3 columns.