python - 函数偶尔返回无，但如果我打印返回它似乎很好

Question

我有一个从 Web 界面提取 json 数据的应用程序。

大多数时候数据都在那里，但有时它不是，或者它多次返回相同的东西。

我已经删除了新行并选择了第一行，并将其分配给一个变量。当我在循环中打印我的函数时，它仍然会打印一些“无”。

如果我在函数中将返回值更改为“打印”，它似乎只打印有效数据，所以我对如何仍然得到“无”返回感到困惑。

功能

def getTest():
    for o in getData():
        if 'system' in o:
            currentValue = o['tag']
            try:
                stripValue = currentValue.splitlines()[0] # grab first line and drop the rest
                print(stripValue)
            except:
                pass

输出

Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]
Talkgroup ID 54638 [0xd56e]

带有'return'的代码

def getTest():
    for o in getData():
        if 'system' in o:
            currentValue = o['tag']
            try:
                stripValue = currentValue.splitlines()[0] # grab first line and drop the rest
                return(stripValue)
            except:
                pass

上述函数的输出

Talkgroup ID 13570 [0x3502]
None
Talkgroup ID 13570 [0x3502]
Talkgroup ID 13570 [0x3502]
Talkgroup ID 13570 [0x3502]
None
Talkgroup ID 13570 [0x3502]

下面是getData函数

def getData(debug=False):
    debug == False
    data = [{'command': 'update', 'data': 0}]
    headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
    r = requests.post("http://pi25.local", data=json.dumps(data), headers=headers)
    if debug == True:
        print(r.status_code, r.reason)
    data = r.json()
    return data

下面是“数据”的输出

请注意，这会发生变化，有时并非所有变量在每次查询时都有值。

[{'nac': 835, 'wacn': 781824, 'tgid': None, 'tdma': None, 'json_type': 'change_freq', 'system': 'P25 SYSTEM', 'sysid': 840, 'tag': '', 'offset': 0, 'stream_url': '', 'freq': 855862500, 'center_frequency': None, 'fine_tune': 0.0}, {'nac': 835, '835': {'rxchan': 855862500, 'txchan': 810862500, 'frequency_data': {'854887500': {'last_activity': '   11.8', 'tgids': [13570, None], 'counter': 1577}, '855787500': {'last_activity': '    5.0', 'tgids': [27672, None], 'counter': 1515}, '855412500': {'last_activity': '    1.0', 'tgids': [13570, None], 'counter': 1729}, '854462500': {'last_activity': '   26.9', 'tgids': [6531, None], 'counter': 1646}, '854437500': {'last_activity': '   34.3', 'tgids': [27550, None], 'counter': 1448}, '854987500': {'last_activity': '   14.4', 'tgids': [54638, None], 'counter': 1706}, '855462500': {'last_activity': '   13.4', 'tgids': [27554, None], 'counter': 1729}, '852575000': {'last_activity': '   14.6', 'tgids': [27500, None], 'counter': 1963}, '856212500': {'last_activity': '   25.8', 'tgids': [54768, None], 'counter': 1510}, '856237500': {'last_activity': '   31.6', 'tgids': [54768, None], 'counter': 1506}, '855937500': {'last_activity': '   28.5', 'tgids': [27617, None], 'counter': 1774}, '854662500': {'last_activity': '    0.4', 'tgids': [54768, None], 'counter': 1547}}, 'tsbks': 84694, 'wacn': 781824, 'frequencies': {'854887500': 'voice frequency 854.887500 tgid(s) 13570 None 11.8s ago count 1577', '855787500': 'voice frequency 855.787500 tgid(s) 27672 None  5.0s ago count 1515', '855412500': 'voice frequency 855.412500 tgid(s) 13570 None  1.0s ago count 1729', '854462500': 'voice frequency 854.462500 tgid(s) 6531 None 26.9s ago count 1646', '854437500': 'voice frequency 854.437500 tgid(s) 27550 None 34.3s ago count 1448', '854987500': 'voice frequency 854.987500 tgid(s) 54638 None 14.4s ago count 1706', '855462500': 'voice frequency 855.462500 tgid(s) 27554 None 13.4s ago count 1729', '852575000': 'voice frequency 852.575000 tgid(s) 27500 None 14.6s ago count 1963', '856212500': 'voice frequency 856.212500 tgid(s) 54768 None 25.8s ago count 1510', '856237500': 'voice frequency 856.237500 tgid(s) 54768 None 31.6s ago count 1506', '855937500': 'voice frequency 855.937500 tgid(s) 27617 None 28.5s ago count 1774', '854662500': 'voice frequency 854.662500 tgid(s) 54768 None  0.4s ago count 1547'}, 'stid': 3, 'rfid': 2, 'last_tsbk': 1558581997.944967, 'adjacent_data': {'774781250': {'table': 1, 'stid': 1, 'rfid': 2, 'uplink': 804781250}, '773556250': {'table': 1, 'stid': 8, 'rfid': 2, 'uplink': 803556250}, '856037500': {'table': 0, 'stid': 10, 'rfid': 2, 'uplink': 811037500}, '771181250': {'table': 1, 'stid': 9, 'rfid': 2, 'uplink': 801181250}}, 'sysid': 840, 'syid': 840, 'secondary': [860762500, 860812500, 860862500]}, 'encrypted': 0, 'json_type': 'trunk_update', 'srcaddr': 0, 'grpaddr': 13570}, {'fine_tune': 0.0, 'files': [], 'json_type': 'rx_update', 'error': 341}]

我找到了一种无需迭代的方法，但我仍然得到这个随机的 None

def test():
    try:
        data = [{'command': 'update', 'data': 0}]
        headers = {'Content-type': 'application/json', 'Accept': 'text/plain'}
        r = requests.post("http://pi25.local", data=json.dumps(data), headers=headers)
        data = r.json()
        return data[0]['tag']
    except:
        pass

while True:
    print(test())

标签： pythonpython-3.x