有没有办法对整个列表使用count（）而不必分别在每个变量上使用它？如果这是可能的话，它将为我节省很多打字。
var1 = random.randint(u,v)
var2 = random.randint(w,x)
var3 = random.randint(y,z)
listName = [var1,var2,var3]
listName.count(x)
listName.count(y) #can you get the count for an entire list instead of having to do them
listName.count(z) #all seperately? It would be much more efficient.
答案 0 :(得分：0)
这是一个创建包含随机内容的列表然后显示长度和总和的示例。
03-10 08:12:38.665 13660-13660/com.example.mypc.inventory W/Bundle: Key id expected String but value was a java.util.HashMap. The default value <null> was returned.
03-10 08:12:38.666 13660-13660/com.example.mypc.inventory W/Bundle: Attempt to cast generated internal exception:
java.lang.ClassCastException: java.util.HashMap cannot be cast to java.lang.String
at android.os.BaseBundle.getString(BaseBundle.java:995)
at android.content.Intent.getStringExtra(Intent.java:6243)
at com.example.mypc.inventory.Inventory_View.onCreate(Inventory_View.java:59)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
03-10 08:12:38.671 13660-13660/com.example.mypc.inventory D/SQLiteHandler: Fetching user from Sqlite: {}
03-10 08:12:38.675 13660-13660/com.example.mypc.inventory D/AndroidRuntime: Shutting down VM
03-10 08:12:38.676 13660-13660/com.example.mypc.inventory E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mypc.inventory, PID: 13660
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mypc.inventory/com.example.mypc.inventory.Inventory_View}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
at com.example.mypc.inventory.Inventory_View.onCreate(Inventory_View.java:61)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
示例输出：
import random
my_list = [
random.randint(1, 10),
random.randint(1, 10),
random.randint(1, 10)
]
print("The value of my_list is {0}".format(my_list))
print("The length of my_list is {0}".format(len(my_list)))
print("The sum of my_list is {0}".format(sum(my_list)))
这是你在找什么？
答案 1 :(得分：0)
list.count(item)返回item在列表中显示的次数。
如果您想知道每个项目在列表中显示的次数，如果它出现在列表中，您可以这样做：
original_list = [1, 1, 2, 3, 4, 4, 4]
uniques = list(set(original_list))
counts = {}
for unique in uniques:
counts[unique] = original_list.count(unique)
print(counts)
应打印类似
的内容{
1: 2,
2: 1,
3: 1,
4: 3
}
以下是set数据类型的更多信息：
https://docs.python.org/3/tutorial/datastructures.html#sets
虽然我们正在使用它，但您也可以使用collections.Counter：
from collections import Counter
counts = Counter([1, 1, 2, 3, 4, 4, 4])
print(dict(counts))
这应该打印与上面相同的字典。