在python字典中的列表中的字典之间进行迭代-根据条件返回值

Question

I want to scrape weather forecast data, more precisely, I want to get data from a dict which has a list with multiple dicts:

  data = {'city': BERLIN,
 'list': [{'date': '2018-10-19 18:00:00',
       'weather': {'temp': 12.86,
                'temp_max': 13.98,
                'temp_min': 12.86},
       'wind': {'deg': 64.5011, 'speed': 1.32}},
      {'date': '2018-10-20 18:00:00',
       'weather': {'temp': 15.86,
                'temp_max': 18.48,
                'temp_min': 12.84},,
       'wind': {'deg': 144.507, 'speed': 1.92}},
    ....

The tricky part is that I want it to return the 'wind' key in the dictionary, where the date is equal to a SATURDAY.

At the end, I'd like to have something like: {Saturday, 'wind': {'deg': 144.507, 'speed': 1.92}}

I have looped through 'list', but am lost how to check for Saturday of the date:

    for item in data.get('list'):
print(item.get('date'))
print(item.get('wind'))

returns:

    2018-10-20 18:00:00
{'speed': 3.92, 'deg': 294.003}
    2018-10-20 21:00:00
{'speed': 3.57, 'deg': 276.001}

To retrieve day and wind keys I tried:

    for item in data.get('list'):
print(item.get(datetime.strptime('date','%Y-%m-%d %H:%M:%S').weekday()))

But get the error that 'time data 'date' does not match format '%Y-%m-%d %H:%M:%S''

Answer 1

you just have your strptime usage a bit wrong, right now you're telling it to extract date data from the string "date" but what you want is to extract date data from the variable item["date"] :

for item in data['list']:
    print(datetime.strptime(item["date"],'%Y-%m-%d %H:%M:%S').weekday()))

you also don't need to use the .get() function of dictionaries it's much easier and more acceptable to use the square brackets notation

Answer 2

You should use item['date'] instead of a literal 'date' to reference the item's 'date' value. The following will return the sub-dict of the wind key of the first Saturday entry:

next((item['wind'] for item in data['list'] if datetime.strptime(item['date'],'%Y-%m-%d %H:%M:%S').weekday() == 5), {})

Answer 3

You want to do three things.

1. Iterate through a list of dictionaries.
2. Convert date to a week day.
3. Check if week day is Saturday .

---

The first step you already got nailed, but you don't need to use get() method to access keys in a dictionary. Using square brackets works too.

for item in data['list']: do something

---

When you are inside the loop you need to grab the value from the date key and then convert it to a datetime object by using the datetime.strptime() function. Now you're doing this on a string with the value date .

You are doing this: datetime.strptime('date','%Y-%m-%d %H:%M:%S')

It should be this: datetime.strptime(item['date'],'%Y-%m-%d %H:%M:%S')

After you have converted the value from the date key you could store it in a variable and use the strftime() method to convert it to a week day string by calling it with %A .

---

The third and last step would be to check if the week day is Saturday . You do this with an IF-statement.

if week_day == 'Saturday': do something

---

Combining all three steps could result in something looking like this:

for item in data['list']:  # step 1

    date = datetime.strptime(item['date'],'%Y-%m-%d %H:%M:%S')  # step 2a
    weekday = date.strftime('%A')  # step 2b

    if weekday == 'Saturday':  # step 3
        print(item)

Answer 4

Thank you antimatter , and especially user347 . I build upon your suggestions and came up with the following. Note that I expanded on it since I want to have data for Sat and Sun and for 12 and 15 o'clock. Is there a good solution for shortening the 4 if-statements?

    for item in data['list']:  

date = datetime.strptime(item['date'],'%Y-%m-%d %H:%M:%S')  
weekday = date.strftime('%A') 
time = date.strftime('%H')

if weekday == 'Saturday' and time == '12':
    if item['wind']['speed'] >= 6 and item['wind']['deg'] >= 180:
        print('Perfect conditions on Saturday at 12 -  wind with ' + 
              str(round(item['wind']['speed']* 1.943846, 1)) + 
              ' knots' + ' and direction: '+ str(item['wind']['deg']))

if weekday == 'Saturday' and time == '15':
    if item['wind']['speed'] >= 6 and item['wind']['deg'] >= 180:
        print('Perfect conditions on Saturday at 15  - wind with ' + 
              str(round(item['wind']['speed']* 1.943846, 1)) + 
              ' knots' + ' and direction: '+ str(item['wind']['deg']))

if weekday == 'Sunday' and time == '12':
    if item['wind']['speed'] >= 6 and item['wind']['deg'] >= 180:
        print('Perfect conditions on Sunday at 12 - wind with ' + 
              str(round(item['wind']['speed']* 1.943846, 1)) + 
              ' knots' + ' and direction: '+ str(item['wind']['deg']))

if weekday == 'Sunday' and time == '15':
    if item['wind']['speed'] >= 6 and item['wind']['deg'] >= 180:
        print('Perfect conditions on Sunday at 12 - wind with ' + 
              str(round(item['wind']['speed']* 1.943846, 1)) + 
              ' knots' + ' and direction: '+ str(item['wind']['deg']))

which returns:

    Perfect conditions on Saturday at 12 - wind with 13.4 knots and direction: 
    306.511
    Perfect conditions on Saturday at 12 - wind with 14.0 knots and direction: 
    306.001