最近在python裡面用json讀取json檔案，可是老是不成功，特此記錄一下。

預備知識：

def load(fp, cls=None, object_hook=None, parse_float=None,
        parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):
    """Deserialize ``fp`` (a ``.read()``-supporting file-like object containing
    a JSON document) to a Python object."""
 



def loads(s, encoding=None, cls=None, object_hook=None, parse_float=None,
        parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):
    """Deserialize ``s`` (a ``str`` instance containing a JSON
    document) to a Python object."""

其實我剛剛看json.load()和json.loads()程式碼定義的時候，也不知道什麼是檔案型別。什麼是字串型別，用python的type函式看一下就好了
例如：

with open("檔名") as f:
     print(type(f))  # <class '_io.TextIOWrapper'>  也就是文字IO型別
     result=json.load(f)

with open("檔名") as f:
    line=f.readline():  
    print(type(line))  # <class 'str'>
    result=json.loads(line)

使用方法

從以上可以看出json.load()是用來讀取檔案的，即，將檔案開啟然後就可以直接讀取。示例如下：

with
 
 open("檔名") as f:
     result=json.load(f)

json.loads()是用來讀取字串的，即，可以把檔案開啟，用readline()讀取一行，然後json.loads()一行。示例如下：

#json檔案為：
{"outputs": ["pool1/7x7/ets", "pool1/7x7/rf", "pool1/10x10/ets", "pool1/10x10/rf", "pool1/13x13/ets", "pool1/13x13/rf"]}

讀取程式碼如下：

with open("檔名") as f:
    line=f.readline():
    result=json.loads(line)

當json檔案如下時，讀取內容是錯誤的：

{
"dataset":{
    "train": {"type": "mnist", "data_set": "train", "layout_x": "tensor"},
    "test": {"type": "mnist", "data_set": "test", "layout_x": "tensor"}
},
"train":{
    "keep_model_in_mem":0,
    "random_state":0,
    "data_cache":{
        "cache_in_disk":{
            "default":1
        },
        "keep_in_mem":{
            "default":0
        },
        "cache_dir":"/mnt/raid/fengji/gcforest/mnist/fg-tree500-depth100-3folds/datas"
    }
},
"net":{
"outputs": ["pool1/7x7/ets", "pool1/7x7/rf", "pool1/10x10/ets", "pool1/10x10/rf", "pool1/13x13/ets", "pool1/13x13/rf"],
"layers":[
    {
        "type":"FGWinLayer",
        "name":"win1/7x7",
        "bottoms": ["X","y"],
        "tops":["win1/7x7/ets", "win1/7x7/rf"],
        "n_classes": 124,
        "estimators": [
            {"n_folds":3,"type":"ExtraTreesClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10},
            {"n_folds":3,"type":"RandomForestClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10}
        ],
        "stride_x": 2,
        "stride_y": 2,
        "win_x":7,
        "win_y":7
    },
    {
        "type":"FGWinLayer",
        "name":"win1/10x10",
        "bottoms": ["X","y"],
        "tops":["win1/10x10/ets", "win1/10x10/rf"],
        "n_classes": 10,
        "estimators": [
            {"n_folds":3,"type":"ExtraTreesClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10},
            {"n_folds":3,"type":"RandomForestClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10}
        ],
        "stride_x": 2,
        "stride_y": 2,
        "win_x":10,
        "win_y":10
    },
    {
        "type":"FGWinLayer",
        "name":"win1/13x13",
        "bottoms": ["X","y"],
        "tops":["win1/13x13/ets", "win1/13x13/rf"],
        "n_classes": 10,
        "estimators": [
            {"n_folds":3,"type":"ExtraTreesClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10},
            {"n_folds":3,"type":"RandomForestClassifier","n_estimators":500,"max_depth":100,"n_jobs":-1,"min_samples_leaf":10}
        ],
        "stride_x": 2,
        "stride_y": 2,
        "win_x":13,
        "win_y":13
    },
    {
        "type":"FGPoolLayer",
        "name":"pool1",
        "bottoms": ["win1/7x7/ets", "win1/7x7/rf", "win1/10x10/ets", "win1/10x10/rf", "win1/13x13/ets", "win1/13x13/rf"],
        "tops": ["pool1/7x7/ets", "pool1/7x7/rf", "pool1/10x10/ets", "pool1/10x10/rf", "pool1/13x13/ets", "pool1/13x13/rf"],
        "pool_method": "avg",
        "win_x":2,
        "win_y":2
    }
]

}
}

因為在程式碼中，json.loads()並沒有讀取完整的json檔案，只是讀取了行，所以這時json.loads(line)讀取的是不合符json語法的字串，會報錯：

with open("檔名") as f:
    line=f.readline():   # 這裡line只是讀取了json檔案的一行，並沒有全部讀取，所以line裡面所存的字串是不符合json語法的，所以讀取出錯。
    result=json.loads(line)

 Traceback (most recent call last):
  File "D:/PycharmProjects/mnistCheck/test.py", line 12, in <module>
    result = json.loads(row)
  File "C:\ProgramData\Anaconda3\envs\tensorflow\lib\json\__init__.py", line 319, in loads
    return _default_decoder.decode(s)
  File "C:\ProgramData\Anaconda3\envs\tensorflow\lib\json\decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:\ProgramData\Anaconda3\envs\tensorflow\lib\json\decoder.py", line 355, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 2 column 1 (char 2)

那麼問題來了。。。。在實際應用中，我們會在json檔案中做註釋，比如以“//”開頭的註釋，除了註釋部分外，其他內容都是符合json語法的，那麼我們要怎麼處理呢？

    def load_json(path):   
    import json
    lines = []     #  第一步：定義一個列表， 開啟檔案
    with open(path) as f:  
        for row in f.readlines(): # 第二步：讀取檔案內容 
            if row.strip().startswith("//"):   # 第三步：對每一行進行過濾 
                continue
            lines.append(row)                   # 第四步：將過濾後的行新增到列表中.
    return json.loads("\n".join(lines))       #將列表中的每個字串用某一個符號拼接為一整個字串，用json.loads()函式載入，這樣就大功告成啦！！

今天的學習就到這裡，明天見！！