Pickling will serialize your list (convert it, and it&#39;s entries to a unique byte string), so you can save it to disk.  You can also use pickle to retrieve your original list, loading from the saved file.

So, first build a list, then use `pickle.dump` to send it to a file...

    Python 3.4.1 (default, May 21 2014, 12:39:51) 
    [GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
    Type &quot;help&quot;, &quot;copyright&quot;, &quot;credits&quot; or &quot;license&quot; for more information.
    &gt;&gt;&gt; mylist = [&#39;I wish to complain about this parrot what I purchased not half an hour ago from this very boutique.&#39;, &quot;Oh yes, the, uh, the Norwegian Blue...What&#39;s,uh...What&#39;s wrong with it?&quot;, &quot;I&#39;ll tell you what&#39;s wrong with it, my lad. &#39;E&#39;s dead, that&#39;s what&#39;s wrong with it!&quot;, &quot;No, no, &#39;e&#39;s uh,...he&#39;s resting.&quot;]
    &gt;&gt;&gt; 
    &gt;&gt;&gt; import pickle
    &gt;&gt;&gt; 
    &gt;&gt;&gt; with open(&#39;parrot.pkl&#39;, &#39;wb&#39;) as f:
    ...   pickle.dump(mylist, f)
    ... 
    &gt;&gt;&gt; 

Then quit and come back later… and open with `pickle.load`...

    Python 3.4.1 (default, May 21 2014, 12:39:51) 
    [GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
    Type &quot;help&quot;, &quot;copyright&quot;, &quot;credits&quot; or &quot;license&quot; for more information.
    &gt;&gt;&gt; import pickle
    &gt;&gt;&gt; with open(&#39;parrot.pkl&#39;, &#39;rb&#39;) as f:
    ...   mynewlist = pickle.load(f)
    ... 
    &gt;&gt;&gt; mynewlist
    [&#39;I wish to complain about this parrot what I purchased not half an hour ago from this very boutique.&#39;, &quot;Oh yes, the, uh, the Norwegian Blue...What&#39;s,uh...What&#39;s wrong with it?&quot;, &quot;I&#39;ll tell you what&#39;s wrong with it, my lad. &#39;E&#39;s dead, that&#39;s what&#39;s wrong with it!&quot;, &quot;No, no, &#39;e&#39;s uh,...he&#39;s resting.&quot;]
    &gt;&gt;&gt;


It is notoriously difficult to get any useful information on CMake as a beginner. So far, I&#39;ve seen a few tutorials on how to set up some very basic project or another. However, none of these explain the reasoning behind *anything* that is shown in them, always leaving many holes to fill.

What does calling CMake on a CMakeLists *mean*? Is it supposed to be called once per build tree or what? How do I use different settings for each build if they all use the same CMakeLists.txt file from the same source?
Why does each subdirectory need its own CMakeLists file? Would it make sense to use CMake on a CMakeLists.txt other than the one at the root of the project? If so, in what cases? 
What&#39;s the difference between specifying how to build an executable or library from the CMakeLists file in their own subdirectory versus doing it in the CMakeLists file at the root of all source?
Can I make a project for Eclipse and another for Visual Studio, just changing the `-G` option when calling CMake? Is that even how it&#39;s used?

None of the tutorials, documentation pages or questions/answers I&#39;ve seen so far give any useful insight towards understanding how to use CMake. The examples are just not thorough. No matter what tutorials I read, I feel like I&#39;m missing something important.

There are many questions asked by CMake newbies like me that don&#39;t ask this explicitly, but that make obvious the fact that, as newbs, we have no idea how to deal with CMake or what to make of it.

How is CMake used?

Django **1.7** introduced [database migrations][1].

When running the unit tests in Django 1.7, it forces a *migrate*, that takes a long time. So I would like to skip the django migrations, and create the database in the final state.


I know that ignoring the migrations can be a bad practice, as that part of the code would not be tested. But that&#39;s not the case: I&#39;m running the full migrations in the CI test server (jenkins). I only want to skip the migrations in my local tests, where the speed matters.


----------


Some context:

Until Django **1.6**, when using South, I used the [*SOUTH_TESTS_MIGRATE*][2] setting:

&gt; By default, South’s syncdb command will also apply migrations if it’s run in non-interactive mode, which includes when you’re running tests - it will run every migration every time you run your tests.
&gt;
&gt; If you want the test runner to use syncdb instead of migrate - for example, if your migrations are taking way too long to apply - simply set SOUTH_TESTS_MIGRATE = False in settings.py.

However, *syncdb* does not exist anymore, now it&#39;s *migrate*.


And from Django **1.8** I&#39;ll use the *[--keepdb][3]* parameter:

&gt; The --keepdb option can be used to preserve the test database between test runs. This has the advantage of skipping both the create and destroy actions which greatly decreases the time to run tests, especially those in a large test suite. If the test database does not exist, it will be created on the first run and then preserved for each subsequent run. Any unapplied migrations will also be applied to the test database before running the test suite.


So this question is limited to Django 1.7.


  [1]: https://docs.djangoproject.com/en/1.7/topics/migrations/
  [2]: http://south.readthedocs.org/en/latest/unittests.html
  [3]: https://docs.djangoproject.com/en/dev/ref/django-admin/#django-admin-option---keepdb

Disable migrations when running unit tests in Django 1.7

I&#39;m trying to save a list of strings, so that it can be accessed later. How can it be achieved using pickle? An illustrative example could help.



Dump a list in a pickle file and retrieve it back later

<p>I'm trying to save a list of strings, so that it can be accessed later. How can it be achieved using pickle? An illustrative example could help.</p>


I am debugging a microcontroller I&#39;ve built which is writing raw HTTP requests line by line.  I am using Flask for my backend and I would like to see the entire request as it appears in this format:

    GET / HTTP/1.1
    Content-length: 123
    User-agent: blah
    ...

I know Flask is based on WSGI. Is there anyway to get this to work with Flask?

Print raw HTTP request in Flask or WSGI

I have a Python script that requires some command line inputs and I am using `argparse` for parsing them. I found the documentation a bit confusing and couldn&#39;t find a way to check for a format in the input parameters. What I mean by checking format is explained with this example script:

    parser.add_argument(&#39;-s&#39;, &quot;--startdate&quot;, help=&quot;The Start Date - format YYYY-MM-DD &quot;, required=True)
    parser.add_argument(&#39;-e&#39;, &quot;--enddate&quot;, help=&quot;The End Date format YYYY-MM-DD (Inclusive)&quot;, required=True)
    parser.add_argument(&#39;-a&#39;, &quot;--accountid&quot;, type=int, help=&#39;Account ID for the account for which data is required (Default: 570)&#39;)
    parser.add_argument(&#39;-o&#39;, &quot;--outputpath&quot;, help=&#39;Directory where output needs to be stored (Default: &#39; + os.path.dirname(os.path.abspath(__file__)))

I need to check for option `-s` and `-e` that the input by the user is in the format `YYYY-MM-DD`. Is there an option in `argparse` that I do not know of which accomplishes this?

Specify date format for Python argparse input arguments

I am doing some geocoding work that I used `selenium` to screen scrape the x-y coordinate I need for address of a location, I imported an xls file to panda dataframe and want to use explicit loop to update the rows which do not have the x-y coordinate, like below:

    for index, row in rche_df.iterrows():
        if isinstance(row.wgs1984_latitude, float):
            row = row.copy()
            target = row.address_chi        
            dict_temp = geocoding(target)
            row.wgs1984_latitude = dict_temp[&#39;lat&#39;]
            row.wgs1984_longitude = dict_temp[&#39;long&#39;]

I have read https://stackoverflow.com/questions/15972264/why-doesnt-this-function-take-after-i-iterrows-over-a-pandas-dataframe and am fully aware that iterrow only gives us a view rather than a copy for editing, but what if I really to update the value row by row? Is `lambda` feasible?

Updating value in iterrow for pandas

What&#39;s the correct way to initialize an ordered dictionary (OD) so that it retains the order of initial data?

    from collections import OrderedDict
    
    # Obviously wrong because regular dict loses order
    d = OrderedDict({&#39;b&#39;:2, &#39;a&#39;:1}) 

    # An OD is represented by a list of tuples, so would this work?
    d = OrderedDict([(&#39;b&#39;,2), (&#39;a&#39;, 1)])

    # What about using a list comprehension, will &#39;d&#39; preserve the order of &#39;l&#39;
    l = [&#39;b&#39;, &#39;a&#39;, &#39;c&#39;, &#39;aa&#39;]
    d = OrderedDict([(i,i) for i in l])

Question: 

- Will an `OrderedDict` preserve the order of a list of tuples, or tuple of tuples or tuple of lists or list of lists etc. passed at the time of initialization (2nd &amp; 3rd example above)?

- How does one go about verifying if `OrderedDict` actually maintains an order? Since a `dict` has an unpredictable order, what if my test vectors luckily have the same initial order as the unpredictable order of a dict? For example, if instead of `d = OrderedDict({&#39;b&#39;:2, &#39;a&#39;:1})` I write `d = OrderedDict({&#39;a&#39;:1, &#39;b&#39;:2})`, I can wrongly conclude that the order is preserved. In this case, I found out that a `dict` is ordered alphabetically, but that may not be always true. What&#39;s a reliable way to use a counterexample to verify whether a data structure preserves order or not, short of trying test vectors repeatedly until one breaks?

P.S. I&#39;ll just leave this here for [reference][1]: &quot;The OrderedDict constructor and update() method both accept keyword arguments, but their order is lost because Python’s function call semantics pass-in keyword arguments using a regular unordered dictionary&quot;

P.P.S : Hopefully, in future, OrderedDict will preserve the order of kwargs also (example 1): http://bugs.python.org/issue16991

  [1]: https://docs.python.org/2.7/library/collections.html#collections.OrderedDict

Right way to initialize an OrderedDict using its constructor such that it retains order of initial data?

I have two numpy arrays with number (Same length), and I want to count how many elements are equal between those two array (equal = same value and position in array)

    A = [1, 2, 3, 4]
    B = [1, 2, 4, 3]

then I want the return value to be 2 (just 1&amp;2 are equal in position and value)


check how many elements are equal in two numpy arrays python

Is there a more elegant way to write this code? 

What I am doing: I have keys and dates. There can be a number of dates assigned to a key and so I am creating a dictionary of lists of dates to represent this. The following code works fine, but I was hoping for a more elegant and Pythonic method. 

    dates_dict = dict() 
    for key,  date in cur:
        if key in dates_dict:
            dates_dict[key].append(date)
        else:
            dates_dict[key] = [date] 

I was expecting the below to work, but I keep getting a NoneType has no attribute append error. 

    dates_dict = dict() 
    for key,  date in cur:
        dates_dict[key] = dates_dict.get(key, []).append(date) 

This probably has something to do with the fact that

    print([].append(1)) 
    None 

but why?

Appending to list in Python dictionary

Hello so I want to multiply the integers inside a list.

For example;

    l = [1, 2, 3]
    l = [1*2, 2*2, 3*2]

output:

    l = [2, 4, 6]


So I was searching online and most of the answers were regarding multiply all the integers with each other such as:

[1*2*3]


How to multiply all integers inside list

I have a list &#39;abc&#39; and a dataframe &#39;df&#39;:

    abc = [&#39;foo&#39;, &#39;bar&#39;]
    df =
        A  B
    0  12  NaN
    1  23  NaN

I want to insert the list into cell 1B, so I want this result:

        A  B
    0  12  NaN
    1  23  [&#39;foo&#39;, &#39;bar&#39;]

Ho can I do that?

1) If I use this:

    df.ix[1,&#39;B&#39;] = abc

I get the following error message:

    ValueError: Must have equal len keys and value when setting with an iterable

because it tries to insert the list (that has two elements) into a row / column but not into a cell.

2) If I use this:

    df.ix[1,&#39;B&#39;] = [abc]

then it inserts a list that has only one element that is the &#39;abc&#39; list ( `[[&#39;foo&#39;, &#39;bar&#39;]]` ).

3) If I use this:

    df.ix[1,&#39;B&#39;] = &#39;, &#39;.join(abc)

then it inserts a string: ( `foo, bar` ) but not a list.

4) If I use this:

    df.ix[1,&#39;B&#39;] = [&#39;, &#39;.join(abc)]

then it inserts a list but it has only one element ( `[&#39;foo, bar&#39;]` ) but not two as I want ( `[&#39;foo&#39;, &#39;bar&#39;]` ).

Thanks for help!

------------
EDIT
------------
My new dataframe and the old list:

    abc = [&#39;foo&#39;, &#39;bar&#39;]
    df2 =
        A    B         C
    0  12  NaN      &#39;bla&#39;
    1  23  NaN  &#39;bla bla&#39;

Another dataframe:

    df3 =
        A    B         C                    D
    0  12  NaN      &#39;bla&#39;  [&#39;item1&#39;, &#39;item2&#39;]
    1  23  NaN  &#39;bla bla&#39;        [11, 12, 13]

I want insert the &#39;abc&#39; list into `df2.loc[1,&#39;B&#39;]` and/or `df3.loc[1,&#39;B&#39;]`.

If the dataframe has columns only with integer values and/or NaN values and/or list values then inserting a list into a cell works perfectly. If the dataframe has columns only with string values and/or NaN values and/or list values then inserting a list into a cell works perfectly. But if the dataframe has columns with integer and string values and other columns then the error message appears if I use this: `df2.loc[1,&#39;B&#39;] = abc` or `df3.loc[1,&#39;B&#39;] = abc`.

Another dataframe:

    df4 =
              A     B
    0      &#39;bla&#39;  NaN
    1  &#39;bla bla&#39;  NaN

These inserts work perfectly: `df.loc[1,&#39;B&#39;] = abc` or `df4.loc[1,&#39;B&#39;] = abc`.


Python pandas insert list into a cell

In C#, if I have a `List&lt;T&gt;`, and I have an object of type `T`, how can I replace a specific item in the `List&lt;T&gt;` with the object of type `T`?

Here is what I have tried:

    List&lt;CustomListItem&gt; customListItems = new List&lt;CustomListItem&gt;();
    CustomListItem customListItem1 = new CustomListItem() { name = &quot;Item 1&quot;, date = DateTime.MinValue};
    CustomListItem customListItem2 = new CustomListItem() { name = &quot;Item 2&quot;, date = DateTime.MinValue };
    CustomListItem customListItem3 = new CustomListItem() { name = &quot;Item 3&quot;, date = DateTime.MinValue };
    
    customListItems.Add(customListItem1);
    customListItems.Add(customListItem2);
    customListItems.Add(customListItem3);
    
    CustomListItem newCustomListItem = new CustomListItem() { name = &quot;Item 4&quot;, date = DateTime.Now };
    
    customListItem2 = customListItems.Where(i=&gt; i.name == &quot;Item 2&quot;).First();
    customListItem2 = newCustomListItem;

In the above code, I want to replace the `customListItem2` with the `newCustomListItem`.

Do I have to remove the item in the list, and then insert the new item? Can I not do a simple assignment of `customListItem2 = newCustomListItem`?

What is the most efficient way of replacing an item in a list with another item?

Thanks in advance

Replace a object in a list of objects

I have a list of lists like this:

    i = [[1, 2, 3], [2, 4, 5], [1, 2, 3], [2, 4, 5]]

I would like to get a list containing &quot;unique&quot; lists (based on their elements) like:

    o = [[1, 2, 3], [2, 4, 5]]

I cannot use `set()` as there are non-hashable elements in the list. Instead, I am doing this:

    o = []
    for e in i:
      if e not in o:
        o.append(e)

Is there an easier way to do this?



How to make a set of lists

I use pickle to dump a file on python 3, and I use pickle to load the file on python 2, the ValueError appears. 

So, python 2 pickle can not load the file dumped by python 3 pickle?

If I want it? How to do?

ValueError: unsupported pickle protocol: 3, python2 pickle can not load the file dumped by python 3 pickle?

I&#39;m trying to create a user system, which uses a setting and Gui module, and when the GUI module requests for the file to load up using pickle, I keep getting an attribute error. this is from the settings module:

    import pickle
    import hashlib
    
    class User(object):
        def __init__(self, fname, lname, dob, gender):
            self.firstname = fname
            self.lastname = lname
            self._dob = dob
            self.gender = gender
            self.type = &#39;General&#39;
            self._username = &#39;&#39;
            self._hashkey = &#39;&#39;
                    
        def Report(self):
            print(&quot;Full Name: {0} {1}\nDate of Birth: {2}\nGender: {3}\nAccess Level: {4}&quot;.format(self.firstname,self.lastname, self._dob, self.gender, self.type))
            print(self._username)
                    
        def Genusername(self):
            self._username = str(str(self._dob)[:2] + self.firstname[:2] + self.lastname[:2])
            saveUsers(users)
    
        def Genhashkey(self, password):
            encoded = password.encode(&#39;utf-8&#39;,&#39;strict&#39;)
            return hashlib.sha256(encoded).hexdigest()
    
        def Verifypassword(self, password):
            if self._hashkey == self.Genhashkey(password):
                return True
            else:
                return False
            
    class SAdmin(User):
        def __init__(self, fname, lname, dob, gender):
            super().__init__(fname, lname, dob, gender)
            self.type = &#39;Stock Admin&#39;
    
    class Manager(User):
        def __init__(self, fname, lname, dob, gender):
            super().__init__(fname, lname, dob, gender)
            self.type = &#39;Manager&#39;
    
    def saveUsers(users):
        with open(&#39;user_data.pkl&#39;, &#39;wb&#39;) as file:
            pickle.dump(users, file, -1) # PICKLE HIGHEST LEVEL PROTOCOL
                    
    def loadUsers(users):
        try:        
            with open(&#39;user_data.pkl&#39;, &#39;rb&#39;) as file:
                temp = pickle.load(file)
                for item in temp:
                    users.append(item)
        except IOError:
            saveUsers([])
                    
    def userReport(users):
        for user in users:
            print(user.firstname, user.lastname)
                    
    def addUser(users):
        fname = input(&#39;What is your First Name?\n &gt; &#39;)
        lname = input(&#39;What is your Last Name?\n &gt; &#39;)
        dob = int(input(&#39;Please enter your date of birth in the following format, example 12211996\n&gt; &#39;))
        gender = input(&quot;What is your gender? &#39;M&#39; or &#39;F&#39;\n &gt;&quot;)
        level = input(&quot;Enter the access level given to this user &#39;G&#39;, &#39;A&#39;, &#39;M&#39;\n &gt; &quot;)
        password = input(&quot;Enter a password:\n &gt; &quot;)
        if level == &#39;G&#39;:
            usertype = User
        if level == &#39;A&#39;:
            usertype = SAdmin
        if level == &#39;M&#39;:
            usertype = Manager
        users.append(usertype(fname, lname, dob, gender))
        user = users[len(users)-1]
        user.Genusername()
        user._hashkey = user.Genhashkey(password)
        saveUsers(users)
         
    def deleteUser(users):
        userReport(users)
        delete = input(&#39;Please type in the First Name of the user do you wish to delete:\n &gt; &#39;)
        for user in users:
            if user.firstname == delete:
                users.remove(user)
        saveUsers(users)
            
    def changePass(users):
        userReport(users)
        change = input(&#39;Please type in the First Name of the user you wish to change the password for :\n &gt; &#39;)
        for user in users:
            if user.firstname == change:
                oldpass = input(&#39;Please type in your old password:\n &gt; &#39;)
                newpass = input(&#39;Please type in your new password:\n &gt; &#39;)
                if user.Verifypassword(oldpass):
                    user._hashkey = user.Genhashkey(newpass)
                    saveUsers(users)
                else:
                    print(&#39;Your old password does not match!&#39;)
    
    def verifyUser(username, password):
        for user in users:
            if user._username == username and user.Verifypassword(password):
                return True
            else:
                return False  
    
    if __name__ == &#39;__main__&#39;:
        users = []
        loadUsers(users)

and this is the GUI module:

    from PyQt4 import QtGui, QtCore
    import Settings
    
    class loginWindow(QtGui.QDialog):    
        def __init__(self):
            super().__init__()        
            self.initUI()
            
        def initUI(self):
            self.lbl1 = QtGui.QLabel(&#39;Username&#39;)
            self.lbl2 = QtGui.QLabel(&#39;Password&#39;)
            self.username = QtGui.QLineEdit()
            self.password = QtGui.QLineEdit()
            
            self.okButton = QtGui.QPushButton(&quot;OK&quot;)
            self.okButton.clicked.connect(self.tryLogin)
            self.cancelButton = QtGui.QPushButton(&quot;Cancel&quot;)
    
            grid = QtGui.QGridLayout()
            grid.setSpacing(10)
    
            grid.addWidget(self.lbl1, 1, 0)
            grid.addWidget(self.username, 1, 1)
            grid.addWidget(self.lbl2, 2, 0)
            grid.addWidget(self.password, 2, 1)
            grid.addWidget(self.okButton, 3, 1)
            grid.addWidget(self.cancelButton, 3, 0)
    
            self.setLayout(grid)
                          
            self.setGeometry(300, 300, 2950, 150)
            self.setWindowTitle(&#39;Login&#39;)
            self.show()
    
        def tryLogin(self):
            print(self.username.text(), self.password.text())
            if Settings.verifyUser(self.username.text(),self.password.text()):
                print(&#39;it Woks&#39;)
            else:
                QtGui.QMessageBox.warning(
                    self, &#39;Error&#39;, &#39;Incorrect Username or Password&#39;)
    
    class Window(QtGui.QMainWindow):
        def __init__(self):
            super().__init__()        
            
    
    if __name__ == &#39;__main__&#39;:
        
        app = QtGui.QApplication(sys.argv)
        users = []
        Settings.loadUsers(users)
        if loginWindow().exec_() == QtGui.QDialog.Accepted:
            window = Window()
            window.show()
            sys.exit(app.exec_())

each user is a class and are put into a list and then the list is saved using pickle when I load up just the settings file and verify the login everything works fine but when I open up the GUI module and try to verify it doesn&#39;t let me, the error I&#39;m getting:

    Traceback (most recent call last):
      File &quot;C:\Users`Program\LoginGUI.py&quot;, line 53, in &lt;module&gt;
        Settings.loadUsers(users)
      File &quot;C:\Users\Program\Settings.py&quot;, line 51, in loadUsers
        temp = pickle.load(file)
    AttributeError: Can&#39;t get attribute &#39;Manager&#39; on &lt;module &#39;__main__&#39; (built-in)&gt;



Unable to load files using pickle and multiple modules

Say I have the list `score = [1,2,3,4,5]` and it gets changed while my program is running. How could I save it to a file so that next time the program is run I can access the changed list as a `list` type? 

I have tried:

    score=[1,2,3,4,5]

    with open(&quot;file.txt&quot;, &#39;w&#39;) as f:
        for s in score:
            f.write(str(s) + &#39;\n&#39;)

    with open(&quot;file.txt&quot;, &#39;r&#39;) as f:
        score = [line.rstrip(&#39;\n&#39;) for line in f]


    print(score)

But this results in the elements in the list being strings not integers.

How to save a list to a file and read it as a list type?

I&#39;m wondering if there is a way to load an object that was pickled in Python 2.4, with Python 3.4.

I&#39;ve been running 2to3 on a large amount of company legacy code to get it up to date.

Having done this, when running the file I get the following error:

      File &quot;H:\fixers - 3.4\addressfixer - 3.4\trunk\lib\address\address_generic.py&quot;
    , line 382, in read_ref_files
        d = pickle.load(open(mshelffile, &#39;rb&#39;))
    UnicodeDecodeError: &#39;ascii&#39; codec can&#39;t decode byte 0xe2 in position 1: ordinal
    not in range(128)

Looking at the pickled object in contention, it&#39;s a `dict` in a `dict`, containing keys and values of type `str`.

So my question is: Is there a way to load an object, originally pickled in python 2.4, with python 3.4?

Unpickling a python 2 object with python 3

I am trying to apply `_pickle` to save data onto disk. But when calling `_pickle.dump`, I got an error
    
    OverflowError: cannot serialize a bytes object larger than 4 GiB

Is this a hard limitation to use `_pickle`? (`cPickle` for python2)

Content Type	Original Author	Original Content on Stackoverflow
Question	Lewis	View Question on Stackoverflow
Solution 1 - Python	Mike McKerns	View Answer on Stackoverflow

Dump a list in a pickle file and retrieve it back later

Python Problem Overview

Python Solutions

Solution 1 - Python

Disable migrations when running unit tests in Django 1.7

How is CMake used?

Attributions