import numpy as np

def movingAvg(x, T):
    """
    Python implementation of the MATLAB movingAvg function.
    Creates a moving average series over T days.
    
    Parameters:
    x (ndarray): Input array for moving average calculation
    T (int): Number of periods to average over
    
    Returns:
    ndarray: Moving average with NaNs in the beginning
    """
    assert T > 0
    
    if isinstance(x, list):
        x = np.array(x)
    
    # Get dimensions
    if len(x.shape) == 1:
        x = x.reshape(-1, 1)
    
    rows, cols = x.shape
    
    # Initialize the result array
    mvavg = np.zeros((rows - T + 1, cols))
    
    # Calculate the sum for each position
    for i in range(T):
        mvavg += x[i:rows-T+1+i, :]
    
    # Divide by T to get the average
    mvavg = mvavg / T
    
    # Add NaNs at the beginning
    result = np.vstack([np.full((T-1, cols), np.nan), mvavg])
    
    # If original input was a vector, return a vector
    if cols == 1 and len(x.shape) == 1:
        result = result.flatten()
        
    return result