问题
How do I see the type of a variable whether it is unsigned 32 bit, signed 16 bit, etc.?
How do I view it?
回答1:
Python doesn't have the same types as C/C++, which appears to be your question.
Try this:
>>> i = 123
>>> type(i)
<type 'int'>
>>> type(i) is int
True
>>> i = 123456789L
>>> type(i)
<type 'long'>
>>> type(i) is long
True
>>> i = 123.456
>>> type(i)
<type 'float'>
>>> type(i) is float
True
The distinction between int and long goes away in Python 3.0, though.
回答2:
You may be looking for the type() function.
See the examples below, but there's no "unsigned" type in Python just like Java.
Positive integer:
>>> v = 10
>>> type(v)
<type 'int'>
Large positive integer:
>>> v = 100000000000000
>>> type(v)
<type 'long'>
Negative integer:
>>> v = -10
>>> type(v)
<type 'int'>
Literal sequence of characters:
>>> v = 'hi'
>>> type(v)
<type 'str'>
Floating point integer:
>>> v = 3.14159
>>> type(v)
<type 'float'>
回答3:
It is so simple. You do it like this.
print(type(variable_name))
回答4:
How to determine the variable type in Python?
So if you have a variable, for example:
one = 1
You want to know its type?
There are right ways and wrong ways to do just about everything in Python. Here's the right way:
Use type
>>> type(one)
<type 'int'>
You can use the __name__ attribute to get the name of the object. (This is one of the few special attributes that you need to use the __dunder__ name to get to - there's not even a method for it in the inspect module.)
>>> type(one).__name__
'int'
Don't use __class__
In Python, names that start with underscores are semantically not a part of the public API, and it's a best practice for users to avoid using them. (Except when absolutely necessary.)
Since type gives us the class of the object, we should avoid getting this directly. :
>>> one.__class__
This is usually the first idea people have when accessing the type of an object in a method - they're already looking for attributes, so type seems weird. For example:
class Foo(object):
def foo(self):
self.__class__
Don't. Instead, do type(self):
class Foo(object):
def foo(self):
type(self)
Implementation details of ints and floats
How do I see the type of a variable whether it is unsigned 32 bit, signed 16 bit, etc.?
In Python, these specifics are implementation details. So, in general, we don't usually worry about this in Python. However, to sate your curiosity...
In Python 2, int is usually a signed integer equal to the implementation's word width (limited by the system). It's usually implemented as a long in C. When integers get bigger than this, we usually convert them to Python longs (with unlimited precision, not to be confused with C longs).
For example, in a 32 bit Python 2, we can deduce that int is a signed 32 bit integer:
>>> import sys
>>> format(sys.maxint, '032b')
'01111111111111111111111111111111'
>>> format(-sys.maxint - 1, '032b') # minimum value, see docs.
'-10000000000000000000000000000000'
In Python 3, the old int goes away, and we just use (Python's) long as int, which has unlimited precision.
We can also get some information about Python's floats, which are usually implemented as a double in C:
>>> sys.float_info
sys.floatinfo(max=1.7976931348623157e+308, max_exp=1024, max_10_exp=308,
min=2.2250738585072014e-308, min_exp=-1021, min_10_exp=-307, dig=15,
mant_dig=53, epsilon=2.2204460492503131e-16, radix=2, rounds=1)
Conclusion
Don't use __class__, a semantically nonpublic API, to get the type of a variable. Use type instead.
And don't worry too much about the implementation details of Python. I've not had to deal with issues around this myself. You probably won't either, and if you really do, you should know enough not to be looking to this answer for what to do.
回答5:
print type(variable_name)
I also highly recommend the IPython interactive interpreter when dealing with questions like this. It lets you type variable_name? and will return a whole list of information about the object including the type and the doc string for the type.
e.g.
In [9]: var = 123
In [10]: var?
Type: int
Base Class: <type 'int'>
String Form: 123
Namespace: Interactive
Docstring:
int(x[, base]) -> integer
Convert a string or number to an integer, if possible. A floating point argument will be truncated towards zero (this does not include a string representation of a floating point number!) When converting a string, use the optional base. It is an error to supply a base when converting a non-string. If the argument is outside the integer range a long object will be returned instead.
回答6:
a = "cool"
type(a)
//result
<class 'str'>
or do `dir(a)` to see the list of inbuilt methods you can have on the variable.
回答7:
One more way using __class__:
>>> a = [1, 2, 3, 4]
>>> a.__class__
<type 'list'>
>>> b = {'key1': 'val1'}
>>> b.__class__
<type 'dict'>
>>> c = 12
>>> c.__class__
<type 'int'>
回答8:
Examples of simple type checking in Python:
assert type(variable_name) == int
assert type(variable_name) == bool
assert type(variable_name) == list
回答9:
It may be little irrelevant. but you can check types of an object with isinstance(object, type) as mentioned here.
回答10:
The question is somewhat ambiguous -- I'm not sure what you mean by "view". If you are trying to query the type of a native Python object, @atzz's answer will steer you in the right direction.
However, if you are trying to generate Python objects that have the semantics of primitive C-types, (such as uint32_t, int16_t), use the struct module. You can determine the number of bits in a given C-type primitive thusly:
>>> struct.calcsize('c') # char
1
>>> struct.calcsize('h') # short
2
>>> struct.calcsize('i') # int
4
>>> struct.calcsize('l') # long
4
This is also reflected in the array module, which can make arrays of these lower-level types:
>>> array.array('c').itemsize # char
1
The maximum integer supported (Python 2's int) is given by sys.maxint.
>>> import sys, math
>>> math.ceil(math.log(sys.maxint, 2)) + 1 # Signedness
32.0
There is also sys.getsizeof, which returns the actual size of the Python object in residual memory:
>>> a = 5
>>> sys.getsizeof(a) # Residual memory.
12
For float data and precision data, use sys.float_info:
>>> sys.float_info
sys.floatinfo(max=1.7976931348623157e+308, max_exp=1024, max_10_exp=308, min=2.2250738585072014e-308, min_exp=-1021, min_10_exp=-307, dig=15, mant_dig=53, epsilon=2.2204460492503131e-16, radix=2, rounds=1)
回答11:
Do you mean in Python or using ctypes?
In the first case, you simply cannot - because Python does not have signed/unsigned, 16/32 bit integers.
In the second case, you can use type():
>>> import ctypes
>>> a = ctypes.c_uint() # unsigned int
>>> type(a)
<class 'ctypes.c_ulong'>
For more reference on ctypes, an its type, see the official documentation.
回答12:
Python doesn't have such types as you describe. There are two types used to represent integral values: int, which corresponds to platform's int type in C, and long, which is an arbitrary precision integer (i.e. it grows as needed and doesn't have an upper limit). ints are silently converted to long if an expression produces result which cannot be stored in int.
回答13:
It really depends on what level you mean. In Python 2.x, there are two integer types, int (constrained to sys.maxint) and long (unlimited precision), for historical reasons. In Python code, this shouldn't make a bit of difference because the interpreter automatically converts to long when a number is too large. If you want to know about the actual data types used in the underlying interpreter, that's implementation dependent. (CPython's are located in Objects/intobject.c and Objects/longobject.c.) To find out about the systems types look at cdleary answer for using the struct module.
回答14:
Simple, for python 3.4 and above
print (type(variable_name))
Python 2.7 and above
print type(variable_name)
回答15:
For python2.x, use
print type(variable_name)
For python3.x, use
print(type(variable_name))
回答16:
Just do not do it. Asking for something's type is wrong in itself. Instead use polymorphism. Find or if necessary define by yourself the method that does what you want for any possible type of input and just call it without asking about anything. If you need to work with built-in types or types defined by a third-party library, you can always inherit from them and use your own derivatives instead. Or you can wrap them inside your own class. This is the object-oriented way to resolve such problems.
If you insist on checking exact type and placing some dirty ifs here and there, you can use __class__ property or type function to do it, but soon you will find yourself updating all these ifs with additional cases every two or three commits. Doing it the OO way prevents that and lets you only define a new class for a new type of input instead.
来源：https://stackoverflow.com/questions/402504/how-to-determine-a-python-variables-type