Python 数据类型无法识别答案

【问题标题】：Python data type not recognizedPython 数据类型无法识别
【发布时间】：2021-12-01 15:52:38
【问题描述】：

我有以下代码。这段代码在仪表板上创建并显示一个 covid 数据。我需要向它添加一个日期选择器并显示适用于该范围的数据。

执行此操作时出现错误“ValueError: format number 1 of "2020-01-01" is not Recognized”。日期选择器输入的值无法转换为日期时间格式，以便我过滤掉记录属于初始数据框的该日期范围。非常感谢任何帮助。

由于这种不匹配，每当我尝试打印接收数据的数据类型或在比较日期的行期间都会遇到错误。

import pandas as pd
from dash import html
import plotly.graph_objects as go
from dash import dcc
import dash
import plotly.express as px
from dash.dependencies import Input, Output
from datetime import date
from datetime import datetime

import datetime

df = pd.read_excel("https://covid.ourworldindata.org/data/owid-covid-data.xlsx")
#
from numpy import dtype

app = dash.Dash()

# df = pd.read_csv('new2.csv', index_col=0)
print(df)
print(df.columns.tolist())
df.drop(
    df.columns.difference(['continent', 'location', 'date', 'total_cases', 'new_cases', 'total_deaths', 'new_deaths']),
    1, inplace=True)
print(df)
df.to_csv('new3.csv', encoding='utf-8', index=False)

app.layout = html.Div(id='parent', children=[

    html.H1(id='H1', children='Covid Dashboard', style={'textAlign': 'center', \
                                                        'marginTop': 40, 'marginBottom': 40}),

    dcc.DatePickerRange(
        id='my-date-picker-range',
        min_date_allowed=date(2020, 1, 1),
        max_date_allowed=date.today(),
        initial_visible_month=date(2020, 1, 1),
        # end_date=date.today()
        display_format='YYYY-MM-DD',
    ),
    html.Div(id='output-container-date-picker-range'),

    dcc.Dropdown(id='dropdown',
                 options=[
                     {'label': 'Total cases', 'value': 'total_cases'},
                     {'label': 'New cases', 'value': 'new_cases'},
                     {'label': 'Total_deaths', 'value': 'total_deaths'},
                     {'label': 'New deaths', 'value': 'new_deaths'},
                 ],
                 value='total_cases'),
    dcc.Graph(id='bar_plot')
])


@app.callback(Output(component_id='bar_plot', component_property='figure'),
              [Input(component_id='dropdown', component_property='value'),
               Input('my-date-picker-range', 'start_date'),
               Input('my-date-picker-range', 'end_date')
               ])
def graph_update(dropdown_value, start_date, end_date):
    print(dropdown_value)
    print(start_date)
    print(end_date)
    start_date1 = '{}'.format(start_date)
    end_date1 = '{}'.format(end_date)


    # to get the world subset since the dataset contains multiple locations
    worldwide_subset = df.loc[df['location'] == 'World']

    if start_date is not None and end_date is not None:
        # date_object = date.fromisoformat(start_date)
        # print(date_object)
        start_date_object = datetime.datetime.strptime(start_date1, '%Y-%m-%d').date()
        end_date_object = datetime.datetime.strptime(end_date1, '%Y-%m-%d').date()
        print('...............')

        
        mask = (df['date'] > start_date_object) & (df['date'] <= end_date_object)
        print(df.loc[mask])
        used_df = df.loc[mask]
        print(used_df)
    else:
        used_df = worldwide_subset

    fig = go.Figure([go.Scatter(x=used_df['date'], y=df['{}'.format(dropdown_value)], \
                                line=dict(color='firebrick', width=4))
                     ])

    fig.update_layout(title=dropdown_value + ' over time',
                      xaxis_title='date',
                      yaxis_title=dropdown_value
                      )
    return fig


if __name__ == '__main__':
    app.run_server()

错误跟踪

[2021-12-01 21:12:24,710] ERROR in app: Exception on /_dash-update-component [POST]
Traceback (most recent call last):
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/flask/app.py", line 2073, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/flask/app.py", line 1518, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/flask/app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/flask/app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/dash/dash.py", line 1336, in dispatch
    response.set_data(func(*args, outputs_list=outputs_list))
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/dash/_callback.py", line 151, in add_context
    output_value = func(*func_args, **func_kwargs)  # %% callback invoked %%
  File "dimi2.py", line 86, in graph_update
    mask = (df['date'] > start_date_object) & (df['date'] <= end_date_object)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/pandas/core/ops/common.py", line 69, in new_method
    return method(self, other)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/pandas/core/arraylike.py", line 48, in __gt__
    return self._cmp_method(other, operator.gt)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/pandas/core/series.py", line 5502, in _cmp_method
    res_values = ops.comparison_op(lvalues, rvalues, op)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/pandas/core/ops/array_ops.py", line 284, in comparison_op
    res_values = comp_method_OBJECT_ARRAY(op, lvalues, rvalues)
  File "/home/sithijathewahettige/PycharmProjects/djangoProject/dash/venv/lib/python3.8/site-packages/pandas/core/ops/array_ops.py", line 73, in comp_method_OBJECT_ARRAY
    result = libops.scalar_compare(x.ravel(), y, op)
  File "pandas/_libs/ops.pyx", line 107, in pandas._libs.ops.scalar_compare
TypeError: '>' not supported between instances of 'str' and 'datetime.date'

【问题讨论】：

你能给出整个跟踪 - 最重要的是哪一行引发了错误？
掩码 = (df['date'] > start_date_object) & (df['date']
df["date"] 大概是一个字符串。尝试在pd.read_excel 之后执行df["date"] = pd.to_datetime(df["date"])

标签： python pandas dataframe plotly-dash

【解决方案1】：

您收到的错误 TypeError: '>' not supported between instances of 'str' and 'datetime.date' 意味着您应该先将字符串 (str) 转换为 date，然后才能过滤它们。这是一个例子：

import pandas as pd
df = pd.DataFrame({
    'date':['2020-01-01','2020-02-02','2020-03-03','2021-12-01']})
print(df)

数据框：

      date
0  2020-01-01
1  2020-02-02
2  2020-03-03
3  2021-12-01

如果你是type(df['date'][0])，那么你会看到它是str，但如果你是pd.to_datetime(df['date'])[0]，那么类型是Timestamp('2020-01-01 00:00:00')

执行pd.to_datetime(df['date']) 将输出：

0   2020-01-01
1   2020-02-02
2   2020-03-03
3   2021-12-01
Name: date, dtype: datetime64[ns]

您可以过滤日期：

df[(df['date'] > '2020-01-20') & (df['date'] < '2021-03-20')]

输出：

         date
1  2020-02-02
2  2020-03-03

【讨论】：