大体过程

1、加载预训练的模型；

2、提取所需要层的权重，并对其进行重命名。比如我们想要第0层和第11层的权重，那么需要将第11层的权重保留下来并且重命名为第1层的名字；

3、更改模型配置文件（保留几层就是几），并且将第11层的权重赋值给第1层；

4、保存模型为pytorch_model.bin；

首先我们来看一下bert具体有哪些权重：

import torch
from transformers import BertTokenizer, BertModel

bertModel = BertModel.from_pretrained('bert-base-chinese', output_hidden_states=True, output_attentions=True)
tokenizer = BertTokenizer.from_pretrained('bert-base-chinese')
for name,param in bertModel.named_parameters():
  print(name, param.shape)


embeddings.word_embeddings.weight torch.Size([21128, 768])
embeddings.position_embeddings.weight torch.Size([512, 768])
embeddings.token_type_embeddings.weight torch.Size([2, 768])
embeddings.LayerNorm.weight torch.Size([768])
embeddings.LayerNorm.bias torch.Size([768])
encoder.layer.0.attention.self.query.weight torch.Size([768, 768])
encoder.layer.0.attention.self.query.bias torch.Size([768])
encoder.layer.0.attention.self.key.weight torch.Size([768, 768])
encoder.layer.0.attention.self.key.bias torch.Size([768])
encoder.layer.0.attention.self.value.weight torch.Size([768, 768])
encoder.layer.0.attention.self.value.bias torch.Size([768])
encoder.layer.0.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.0.attention.output.dense.bias torch.Size([768])
encoder.layer.0.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.0.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.0.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.0.intermediate.dense.bias torch.Size([3072])
encoder.layer.0.output.dense.weight torch.Size([768, 3072])
encoder.layer.0.output.dense.bias torch.Size([768])
encoder.layer.0.output.LayerNorm.weight torch.Size([768])
encoder.layer.0.output.LayerNorm.bias torch.Size([768])
encoder.layer.1.attention.self.query.weight torch.Size([768, 768])
encoder.layer.1.attention.self.query.bias torch.Size([768])
encoder.layer.1.attention.self.key.weight torch.Size([768, 768])
encoder.layer.1.attention.self.key.bias torch.Size([768])
encoder.layer.1.attention.self.value.weight torch.Size([768, 768])
encoder.layer.1.attention.self.value.bias torch.Size([768])
encoder.layer.1.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.1.attention.output.dense.bias torch.Size([768])
encoder.layer.1.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.1.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.1.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.1.intermediate.dense.bias torch.Size([3072])
encoder.layer.1.output.dense.weight torch.Size([768, 3072])
encoder.layer.1.output.dense.bias torch.Size([768])
encoder.layer.1.output.LayerNorm.weight torch.Size([768])
encoder.layer.1.output.LayerNorm.bias torch.Size([768])
encoder.layer.2.attention.self.query.weight torch.Size([768, 768])
encoder.layer.2.attention.self.query.bias torch.Size([768])
encoder.layer.2.attention.self.key.weight torch.Size([768, 768])
encoder.layer.2.attention.self.key.bias torch.Size([768])
encoder.layer.2.attention.self.value.weight torch.Size([768, 768])
encoder.layer.2.attention.self.value.bias torch.Size([768])
encoder.layer.2.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.2.attention.output.dense.bias torch.Size([768])
encoder.layer.2.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.2.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.2.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.2.intermediate.dense.bias torch.Size([3072])
encoder.layer.2.output.dense.weight torch.Size([768, 3072])
encoder.layer.2.output.dense.bias torch.Size([768])
encoder.layer.2.output.LayerNorm.weight torch.Size([768])
encoder.layer.2.output.LayerNorm.bias torch.Size([768])
encoder.layer.3.attention.self.query.weight torch.Size([768, 768])
encoder.layer.3.attention.self.query.bias torch.Size([768])
encoder.layer.3.attention.self.key.weight torch.Size([768, 768])
encoder.layer.3.attention.self.key.bias torch.Size([768])
encoder.layer.3.attention.self.value.weight torch.Size([768, 768])
encoder.layer.3.attention.self.value.bias torch.Size([768])
encoder.layer.3.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.3.attention.output.dense.bias torch.Size([768])
encoder.layer.3.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.3.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.3.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.3.intermediate.dense.bias torch.Size([3072])
encoder.layer.3.output.dense.weight torch.Size([768, 3072])
encoder.layer.3.output.dense.bias torch.Size([768])
encoder.layer.3.output.LayerNorm.weight torch.Size([768])
encoder.layer.3.output.LayerNorm.bias torch.Size([768])
encoder.layer.4.attention.self.query.weight torch.Size([768, 768])
encoder.layer.4.attention.self.query.bias torch.Size([768])
encoder.layer.4.attention.self.key.weight torch.Size([768, 768])
encoder.layer.4.attention.self.key.bias torch.Size([768])
encoder.layer.4.attention.self.value.weight torch.Size([768, 768])
encoder.layer.4.attention.self.value.bias torch.Size([768])
encoder.layer.4.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.4.attention.output.dense.bias torch.Size([768])
encoder.layer.4.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.4.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.4.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.4.intermediate.dense.bias torch.Size([3072])
encoder.layer.4.output.dense.weight torch.Size([768, 3072])
encoder.layer.4.output.dense.bias torch.Size([768])
encoder.layer.4.output.LayerNorm.weight torch.Size([768])
encoder.layer.4.output.LayerNorm.bias torch.Size([768])
encoder.layer.5.attention.self.query.weight torch.Size([768, 768])
encoder.layer.5.attention.self.query.bias torch.Size([768])
encoder.layer.5.attention.self.key.weight torch.Size([768, 768])
encoder.layer.5.attention.self.key.bias torch.Size([768])
encoder.layer.5.attention.self.value.weight torch.Size([768, 768])
encoder.layer.5.attention.self.value.bias torch.Size([768])
encoder.layer.5.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.5.attention.output.dense.bias torch.Size([768])
encoder.layer.5.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.5.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.5.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.5.intermediate.dense.bias torch.Size([3072])
encoder.layer.5.output.dense.weight torch.Size([768, 3072])
encoder.layer.5.output.dense.bias torch.Size([768])
encoder.layer.5.output.LayerNorm.weight torch.Size([768])
encoder.layer.5.output.LayerNorm.bias torch.Size([768])
encoder.layer.6.attention.self.query.weight torch.Size([768, 768])
encoder.layer.6.attention.self.query.bias torch.Size([768])
encoder.layer.6.attention.self.key.weight torch.Size([768, 768])
encoder.layer.6.attention.self.key.bias torch.Size([768])
encoder.layer.6.attention.self.value.weight torch.Size([768, 768])
encoder.layer.6.attention.self.value.bias torch.Size([768])
encoder.layer.6.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.6.attention.output.dense.bias torch.Size([768])
encoder.layer.6.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.6.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.6.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.6.intermediate.dense.bias torch.Size([3072])
encoder.layer.6.output.dense.weight torch.Size([768, 3072])
encoder.layer.6.output.dense.bias torch.Size([768])
encoder.layer.6.output.LayerNorm.weight torch.Size([768])
encoder.layer.6.output.LayerNorm.bias torch.Size([768])
encoder.layer.7.attention.self.query.weight torch.Size([768, 768])
encoder.layer.7.attention.self.query.bias torch.Size([768])
encoder.layer.7.attention.self.key.weight torch.Size([768, 768])
encoder.layer.7.attention.self.key.bias torch.Size([768])
encoder.layer.7.attention.self.value.weight torch.Size([768, 768])
encoder.layer.7.attention.self.value.bias torch.Size([768])
encoder.layer.7.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.7.attention.output.dense.bias torch.Size([768])
encoder.layer.7.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.7.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.7.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.7.intermediate.dense.bias torch.Size([3072])
encoder.layer.7.output.dense.weight torch.Size([768, 3072])
encoder.layer.7.output.dense.bias torch.Size([768])
encoder.layer.7.output.LayerNorm.weight torch.Size([768])
encoder.layer.7.output.LayerNorm.bias torch.Size([768])
encoder.layer.8.attention.self.query.weight torch.Size([768, 768])
encoder.layer.8.attention.self.query.bias torch.Size([768])
encoder.layer.8.attention.self.key.weight torch.Size([768, 768])
encoder.layer.8.attention.self.key.bias torch.Size([768])
encoder.layer.8.attention.self.value.weight torch.Size([768, 768])
encoder.layer.8.attention.self.value.bias torch.Size([768])
encoder.layer.8.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.8.attention.output.dense.bias torch.Size([768])
encoder.layer.8.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.8.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.8.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.8.intermediate.dense.bias torch.Size([3072])
encoder.layer.8.output.dense.weight torch.Size([768, 3072])
encoder.layer.8.output.dense.bias torch.Size([768])
encoder.layer.8.output.LayerNorm.weight torch.Size([768])
encoder.layer.8.output.LayerNorm.bias torch.Size([768])
encoder.layer.9.attention.self.query.weight torch.Size([768, 768])
encoder.layer.9.attention.self.query.bias torch.Size([768])
encoder.layer.9.attention.self.key.weight torch.Size([768, 768])
encoder.layer.9.attention.self.key.bias torch.Size([768])
encoder.layer.9.attention.self.value.weight torch.Size([768, 768])
encoder.layer.9.attention.self.value.bias torch.Size([768])
encoder.layer.9.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.9.attention.output.dense.bias torch.Size([768])
encoder.layer.9.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.9.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.9.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.9.intermediate.dense.bias torch.Size([3072])
encoder.layer.9.output.dense.weight torch.Size([768, 3072])
encoder.layer.9.output.dense.bias torch.Size([768])
encoder.layer.9.output.LayerNorm.weight torch.Size([768])
encoder.layer.9.output.LayerNorm.bias torch.Size([768])
encoder.layer.10.attention.self.query.weight torch.Size([768, 768])
encoder.layer.10.attention.self.query.bias torch.Size([768])
encoder.layer.10.attention.self.key.weight torch.Size([768, 768])
encoder.layer.10.attention.self.key.bias torch.Size([768])
encoder.layer.10.attention.self.value.weight torch.Size([768, 768])
encoder.layer.10.attention.self.value.bias torch.Size([768])
encoder.layer.10.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.10.attention.output.dense.bias torch.Size([768])
encoder.layer.10.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.10.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.10.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.10.intermediate.dense.bias torch.Size([3072])
encoder.layer.10.output.dense.weight torch.Size([768, 3072])
encoder.layer.10.output.dense.bias torch.Size([768])
encoder.layer.10.output.LayerNorm.weight torch.Size([768])
encoder.layer.10.output.LayerNorm.bias torch.Size([768])
encoder.layer.11.attention.self.query.weight torch.Size([768, 768])
encoder.layer.11.attention.self.query.bias torch.Size([768])
encoder.layer.11.attention.self.key.weight torch.Size([768, 768])
encoder.layer.11.attention.self.key.bias torch.Size([768])
encoder.layer.11.attention.self.value.weight torch.Size([768, 768])
encoder.layer.11.attention.self.value.bias torch.Size([768])
encoder.layer.11.attention.output.dense.weight torch.Size([768, 768])
encoder.layer.11.attention.output.dense.bias torch.Size([768])
encoder.layer.11.attention.output.LayerNorm.weight torch.Size([768])
encoder.layer.11.attention.output.LayerNorm.bias torch.Size([768])
encoder.layer.11.intermediate.dense.weight torch.Size([3072, 768])
encoder.layer.11.intermediate.dense.bias torch.Size([3072])
encoder.layer.11.output.dense.weight torch.Size([768, 3072])
encoder.layer.11.output.dense.bias torch.Size([768])
encoder.layer.11.output.LayerNorm.weight torch.Size([768])
encoder.layer.11.output.LayerNorm.bias torch.Size([768])
pooler.dense.weight torch.Size([768, 768])
pooler.dense.bias torch.Size([768])

完整代码：

import os
import json
import torch
import time
from transformers import BertModel,BertTokenizer

# 提取我们想要的层的权重并重命名
def get_prune_paramerts(model):
    prune_paramerts = {}
    for name, param in model.named_parameters():
        if 'embeddings' in name:
            prune_paramerts[name] = param
        elif name.startswith('encoder.layer.0.'):
            prune_paramerts[name] = param
        elif name.startswith('encoder.layer.11.'):
            pro_name = name.split('encoder.layer.11.')
            prune_paramerts['encoder.layer.1.' + pro_name[1]] = param
        elif 'pooler' in name:
            prune_paramerts[name] = param
    return prune_paramerts

# 修改配置文件
def get_prune_config(config):
    prune_config = config
    prune_config['num_hidden_layers'] = 2
    return prune_config

# 缩减模型的层数，并为相对应的层重新进行权重赋值
def get_prune_model(model, prune_parameters):
    prune_model = model.state_dict()
    for name in list(prune_model.keys()):
        if 'embeddings.position_ids' == name:
            continue
        if 'embeddings' in name:
            prune_model[name] = prune_parameters[name]
        elif name.startswith('encoder.layer.0.'):
            prune_model[name] = prune_parameters[name]
        elif name.startswith('encoder.layer.1.'):
            prune_model[name] = prune_parameters[name]
        elif 'pooler' in name:
            prune_model[name] = prune_parameters[name]
        else:
            del prune_model[name]
    return prune_model

def prune_main():
    model_path = '/data02/gob/project/simpleNLP/model_hub/chinese-bert-wwm-ext/'
    tokenizer = BertTokenizer.from_pretrained(model_path + 'vocab.txt')
    config = json.loads(open(model_path + 'config.json', 'r').read())
    model = BertModel.from_pretrained(model_path)
    text = '我喜欢吃鱼'
    inputs = tokenizer(text, return_tensors='pt')
    # print(model(**inputs))

    out_path = '/data02/gob/project/simpleNLP/model_hub/prune-chinese-bert-wwm-ext/'
    if not os.path.exists(out_path):
        os.makedirs(out_path)
    prune_parameters = get_prune_paramerts(model)
    prune_config = get_prune_config(config)
    prune_model = get_prune_model(model, prune_parameters)
    """
    for name,param in model.named_parameters():
        print(name)
    print("===================================")
    for k,v in model.state_dict().items():
        print(k)
    """
    torch.save(prune_model, out_path + 'pytorch_model.bin')
    with open(out_path + 'config.json', 'w') as fp:
        fp.write(json.dumps(prune_config))
    with open(out_path + 'vocab.txt', 'w') as fp:
        fp.write(open(model_path + 'vocab.txt').read())

if __name__ == '__main__':
    # prune_main()
    start_time = time.time()
    # 之后我们就可以像加载bert模型一样加载剪枝层后的模型
    model_path = '/data02/gob/project/simpleNLP/model_hub/prune-chinese-bert-wwm-ext/'
    tokenizer = BertTokenizer.from_pretrained(model_path + 'vocab.txt')
    config = json.loads(open(model_path + 'config.json', 'r').read())
    model = BertModel.from_pretrained(model_path)
    text = '我喜欢吃鱼'
    inputs = tokenizer(text, return_tensors='pt')
    for name, param in model.named_parameters():
        print(name, param.shape)
    end_time = time.time()
    print('预测耗时：{}s'.format(end_time-start_time))

1、加载预训练的模型；

2、提取所需要层的权重，并选择topk的值进行裁剪，并重新赋值给该层的参数；

3、更改模型配置文件（主要是修改维度）；

4、保存模型为pytorch_model.bin；

具体代码：

import os
import json
import torch
import time
from pprint import pprint
from transformers import BertModel,BertTokenizer

def get_prune_ffn_paramerts(model):
    prune_paramerts = {}
    for name, param in model.named_parameters():
        if 'intermediate.dense.weight' in name:
            param = torch.tensor(param.T.topk(384).values, requires_grad=True).T
            prune_paramerts[name] = param
        elif 'intermediate.dense.bias' in name:
            param = torch.tensor(param.topk(384).values, requires_grad=True)
            prune_paramerts[name] = param
        elif 'output.dense.weight' in name and 'attention.output.dense.weight' not in name:
            param = torch.tensor(param.topk(384).values, requires_grad=True)
            prune_paramerts[name] = param
    return prune_paramerts

def get_prune_ffn_config(config):
    prune_config = config
    prune_config['intermediate_size'] = 384
    return prune_config

def get_prune_model(model, prune_parameters):
    prune_model = model.state_dict()
    for name in list(prune_model.keys()):
        if name in prune_parameters:
            prune_model[name] = prune_parameters[name]
    return prune_model

def prune_main():
    model_path = '/data02/gob/project/simpleNLP/model_hub/prune-chinese-bert-wwm-ext/'
    tokenizer = BertTokenizer.from_pretrained(model_path + 'vocab.txt')
    config = json.loads(open(model_path + 'config.json', 'r').read())
    model = BertModel.from_pretrained(model_path)

    out_path = '/data02/gob/project/simpleNLP/model_hub/prune-ffn-chinese-bert-wwm-ext/'
    if not os.path.exists(out_path):
        os.makedirs(out_path)
    prune_parameters = get_prune_ffn_paramerts(model)
    prune_config = get_prune_ffn_config(config)
    prune_model = get_prune_model(model, prune_parameters)
    torch.save(prune_model, out_path + 'pytorch_model.bin')
    with open(out_path + 'config.json', 'w') as fp:
        fp.write(json.dumps(prune_config))
    with open(out_path + 'vocab.txt', 'w') as fp:
        fp.write(open(model_path + 'vocab.txt').read())

if __name__ == '__main__':
    # prune_main()
    if torch.cuda.is_available():
        device = torch.device('cuda')
    else:
        device = torch.device('cpu')
    model_path = '/data02/gob/project/simpleNLP/model_hub/prune-chinese-bert-wwm-ext/'
    # model_path = '/data02/gob/project/simpleNLP/model_hub/bert-base-chinese/'
    tokenizer = BertTokenizer.from_pretrained(model_path + 'vocab.txt')
    config = json.loads(open(model_path + 'config.json', 'r').read())
    model = BertModel.from_pretrained(model_path)
    model.to(device)
    start_time = time.time()
    texts = ['我喜欢吃鱼,我也喜欢打篮球，你知不知道呀。在这个阳光明媚的日子里，我们一起去放风筝'] * 5000
    for text in texts:
        inputs = tokenizer(text, return_tensors='pt')
        for k in inputs.keys():
            inputs[k] = inputs[k].to(device)
        # pprint(inputs)
        # for name, param in model.named_parameters():
        #     print(name, param.shape)
    end_time = time.time()
    print('预测耗时：{}s'.format(end_time-start_time))

相对复杂，暂时就不考虑了，一般情况下对层数进行剪枝，简单又方便。