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Why are these constructs using pre and post-increment undefined behavior?
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C has the concept of undefined behavior, i.e. some language constructs are syntactically valid but you can't predict the behavior when the code is run.
As far as I know, the standard doesn't explicitly say why the concept of undefined behavior exists. In ...
How can I tell if one commit is a descendant of another commit?
With Git, how can I tell if one commit in my branch is a descendant of another commit?
8 Answers
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What does |= (ior) do in Python?
Google won't let me search |= so I'm having trouble finding relevant documentation. Anybody know?
8 Answers
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Named Branches vs Multiple Repositories
We're currently using subversion on a relatively large codebase. Each release gets its own branch, and fixes are performed against the trunk and migrated into release branches using svnmerge.py
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Removing duplicate objects with Underscore for Javascript
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.uniq/.unique accepts a callback
var list = [{a:1,b:5},{a:1,c:5},{a:2},{a:3},{a:4},{a:3},{a:2}];
var uniqueList = _.uniq(list, function(item, key, a) {
return item.a;
});
// uniqueList = [Object {a=1, b=5}, Object {a=2}, Object {a=3}, Object {a=...
How to send email to multiple recipients using python smtplib?
After much searching I couldn't find out how to use smtplib.sendmail to send to multiple recipients. The problem was every time the mail would be sent the mail headers would appear to contain multiple addresses, but in fact only the first recipient would receive the email.
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How do you create nested dict in Python?
...type 'dict'>, {'dict1': {'innerkey': 'value'}})
>>> dict(d) # but is exactly like a normal dictionary.
{'dict1': {'innerkey': 'value'}}
You can populate that however you want.
I would recommend in your code something like the following:
d = {} # can use defaultdict(dict) instead
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Python-equivalent of short-form “if” in C++ [duplicate]
Is there a way to write this C/C++ code in Python?
a = (b == true ? "123" : "456" )
4 Answers
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Use a list of values to select rows from a pandas dataframe [duplicate]
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You can use isin method:
In [1]: df = pd.DataFrame({'A': [5,6,3,4], 'B': [1,2,3,5]})
In [2]: df
Out[2]:
A B
0 5 1
1 6 2
2 3 3
3 4 5
In [3]: df[df['A'].isin([3, 6])]
Out[3]:
A B
1 6 2
2 3 3
And to get the opposite use ~:
In [4]: df[~df['A'].isin([3, 6])]
Out[4]:
A B...
error: cannot dynamic_cast ‘b’ (of type ‘class Base*’) to type ‘c...
error: cannot dynamic_cast ‘b’ (of type ‘class Base*’) to type ‘class Derived*’ (source type is not polymorphic)在将父类型转换为子类型时,可以使用static_cast和dynamic_cast.如果使用dynamic_cast,它要求父类必须为多态的,即要求至少有一个虚函数,因此....