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copied!<p>In Python there are several types of arguments:</p> <ul> <li>positional and keyword</li> <li>named and arbitrary</li> </ul> <p>The function argument in Python is an attribution operation, that is, arguments are assigned to variables in the function local namespace.</p> <p>If you have a declaration like this:</p> <pre><code>def some_func(pos_arg1, pos_arg2, kw_arg1=1, kw_arg2='test'): print "postional arg 1 =", pos_arg1 print "postional arg 2 =", pos_arg2 print "keyword arg 1 =", kw_arg1 print "keyword arg 2 =", kw_arg2 </code></pre> <p>Positional arguments are mandatory and will be assigned in the given order, but keyword arguments are optional and can be called in any order - when omitted, named keyword arguments assume the declared default values (1 and 'test' in the example). So far:</p> <pre><code>>>> some_func(1) # positional arguments are mandatory Traceback (most recent call last): File "<interactive input>", line 1, in <module> TypeError: some_func() takes at least 2 arguments (1 given) >>> some_func(1, 2) # this is ok postional arg 1 = 1 postional arg 2 = 2 keyword arg 1 = 1 keyword arg 2 = test >>> some_func(1, 2, 3) # this is also ok, keyword args may work like positional postional arg 1 = 1 postional arg 2 = 2 keyword arg 1 = 3 keyword arg 2 = test >>> some_func(1, 2, 3, 4) # this is also ok, keyword args may work like positional postional arg 1 = 1 postional arg 2 = 2 keyword arg 1 = 3 keyword arg 2 = 4 >>> some_func(1, 2, kw_arg2=3) # kyword arguments may be given in any order postional arg 1 = 1 postional arg 2 = 2 keyword arg 1 = 1 keyword arg 2 = 3 </code></pre> <p>There is a problem with undeclared arguments:</p> <pre><code>>>> some_func(1, 2, 3, 4, 5) Traceback (most recent call last): File "<interactive input>", line 1, in <module> TypeError: some_func() takes at most 4 arguments (5 given) </code></pre> <p>But you can have an arbitrary number of arguments in using the special form <code>*</code> and <code>**</code>:</p> <pre><code>>>> def some_func(pos_arg1, pos_arg2, *args, **kw_args): ... print "postional arg 1 =", pos_arg1 ... print "postional arg 2 =", pos_arg2 ... print "other positional orgs =", args ... print "other keyword args =", kw_args ... >>> some_func(1, 2, 3, 4, 5) # any number of arguments postional arg 1 = 1 postional arg 2 = 2 other positional orgs = (3, 4, 5) other keyword args = {} >>> some_func(1, 2, a=3, x=4, y=5) # * and ** are optional postional arg 1 = 1 postional arg 2 = 2 other positional orgs = () other keyword args = {'a': 3, 'x': 4, 'y': 5} >>> some_func(1, 2, 'banana', 'orange', 'apple', a=3, x=4, y=5) postional arg 1 = 1 postional arg 2 = 2 other positional orgs = ('banana', 'orange', 'apple') other keyword args = {'a': 3, 'x': 4, 'y': 5} >>> </code></pre> <p>The <code>*</code> argument will be available as a tuple of positional arguments, and <code>**</code> will be a dict of keyword arguments.</p> <p>You can mix everything together but there is a rule: all keyword arguments have to be declared after positional arguments, and all the arbitrary must be after named ones.</p>

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