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1 | 1 | .. _tutorial: |
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2 | 2 | |
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3 | 3 | ====================== |
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4 | 4 | Introducing IPython |
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5 | 5 | ====================== |
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6 | 6 | |
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7 | 7 | You don't need to know anything beyond Python to start using IPython β just type |
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8 | 8 | commands as you would at the standard Python prompt. But IPython can do much |
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9 | 9 | more than the standard prompt. Some key features are described here. For more |
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10 | 10 | information, check the :ref:`tips page <tips>`, or look at examples in the |
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11 | 11 | `IPython cookbook <https://github.com/ipython/ipython/wiki/Cookbook%3A-Index>`_. |
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12 | 12 | |
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13 | 13 | If you haven't done that yet see :ref:`how to install ipython <install>`. |
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14 | 14 | |
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15 | 15 | If you've never used Python before, you might want to look at `the official |
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16 |
tutorial <http://docs.python.org/tutorial/>`_ |
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17 | Python <https://www.diveinto.org/python3/table-of-contents.html>`_. | |
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16 | tutorial <http://docs.python.org/tutorial/>`_. | |
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18 | 17 | |
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19 | 18 | Start IPython by issuing the ``ipython`` command from your shell, you should be |
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20 | 19 | greeted by the following:: |
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21 | 20 | |
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22 | 21 | Python 3.6.0 |
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23 | 22 | Type 'copyright', 'credits' or 'license' for more information |
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24 | 23 | IPython 6.0.0.dev -- An enhanced Interactive Python. Type '?' for help. |
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25 | 24 | |
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26 | 25 | In [1]: |
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27 | 26 | |
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28 | 27 | |
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29 | 28 | Unlike the Python REPL, you will see that the input prompt is ``In [N]:`` |
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30 | 29 | instead of ``>>>``. The number ``N`` in the prompt will be used later in this |
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31 | 30 | tutorial but should usually not impact the computation. |
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32 | 31 | |
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33 | 32 | You should be able to type single line expressions and press enter to evaluate |
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34 | 33 | them. If an expression is incomplete, IPython will automatically detect this and |
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35 | 34 | add a new line when you press :kbd:`Enter` instead of executing right away. |
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36 | 35 | |
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37 | 36 | Feel free to explore multi-line text input. Unlike many other REPLs, with |
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38 | 37 | IPython you can use the up and down arrow keys when editing multi-line |
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39 | 38 | code blocks. |
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40 | 39 | |
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41 | 40 | Here is an example of a longer interaction with the IPython REPL, |
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42 | 41 | which we often refer to as an IPython *session* :: |
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43 | 42 | |
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44 | 43 | In [1]: print('Hello IPython') |
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45 | 44 | Hello IPython |
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46 | 45 | |
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47 | 46 | In [2]: 21 * 2 |
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48 | 47 | Out[2]: 42 |
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49 | 48 | |
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50 | 49 | In [3]: def say_hello(name): |
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51 | 50 | ...: print('Hello {name}'.format(name=name)) |
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52 | 51 | ...: |
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53 | 52 | |
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54 | 53 | We won't get into details right now, but you may notice a few differences to |
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55 | 54 | the standard Python REPL. First, your code should be syntax-highlighted as you |
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56 | 55 | type. Second, you will see that some results will have an ``Out[N]:`` prompt, |
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57 | 56 | while some other do not. We'll come to this later. |
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58 | 57 | |
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59 | 58 | Depending on the exact command you are typing you might realize that sometimes |
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60 | 59 | :kbd:`Enter` will add a new line, and sometimes it will execute the current |
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61 | 60 | statement. IPython tries to guess what you are doing, so most of the time you |
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62 | 61 | should not have to care. Though if by any chance IPython does not do the right |
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63 | 62 | thing you can force execution of the current code block by pressing in sequence |
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64 | 63 | :kbd:`Esc` and :kbd:`Enter`. You can also force the insertion of a new line at |
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65 | 64 | the position of the cursor by using :kbd:`Ctrl-o`. |
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66 | 65 | |
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67 | 66 | The four most helpful commands |
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68 | 67 | ============================== |
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69 | 68 | |
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70 | 69 | The four most helpful commands, as well as their brief description, is shown |
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71 | 70 | to you in a banner, every time you start IPython: |
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72 | 71 | |
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73 | 72 | ========== ========================================================= |
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74 | 73 | command description |
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75 | 74 | ========== ========================================================= |
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76 | 75 | ? Introduction and overview of IPython's features. |
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77 | 76 | %quickref Quick reference. |
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78 | 77 | help Python's own help system. |
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79 | 78 | object? Details about 'object', use 'object??' for extra details. |
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80 | 79 | ========== ========================================================= |
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81 | 80 | |
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82 | 81 | Tab completion |
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83 | 82 | ============== |
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84 | 83 | |
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85 | 84 | Tab completion, especially for attributes, is a convenient way to explore the |
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86 | 85 | structure of any object you're dealing with. Simply type ``object_name.<TAB>`` |
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87 | 86 | to view the object's attributes. Besides Python objects and keywords, tab |
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88 | 87 | completion also works on file and directory names. |
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89 | 88 | |
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90 | 89 | Starting with IPython 6.0, if ``jedi`` is installed, IPython will try to pull |
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91 | 90 | completions from Jedi as well. This allows to not only inspect currently |
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92 | 91 | existing objects, but also to infer completion statically without executing |
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93 | 92 | code. There is nothing particular needed to get this to work, simply use tab |
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94 | 93 | completion on more complex expressions like the following:: |
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95 | 94 | |
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96 | 95 | >>> data = ['Number of users', 123456] |
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97 | 96 | ... data[0].<tab> |
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98 | 97 | |
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99 | 98 | IPython and Jedi will be able to infer that ``data[0]`` is actually a string |
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100 | 99 | and should show relevant completions like ``upper()``, ``lower()`` and other |
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101 | 100 | string methods. You can use the :kbd:`Tab` key to cycle through completions, |
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102 | 101 | and while a completion is highlighted, its type will be shown as well. |
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103 | 102 | When the type of the completion is a function, the completer will also show the |
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104 | 103 | signature of the function when highlighted. |
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105 | 104 | |
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106 | 105 | Exploring your objects |
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107 | 106 | ====================== |
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108 | 107 | |
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109 | 108 | Typing ``object_name?`` will print all sorts of details about any object, |
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110 | 109 | including docstrings, function definition lines (for call arguments) and |
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111 | 110 | constructor details for classes. To get specific information on an object, you |
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112 | 111 | can use the magic commands ``%pdoc``, ``%pdef``, ``%psource`` and ``%pfile`` |
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113 | 112 | |
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114 | 113 | .. _magics_explained: |
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115 | 114 | |
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116 | 115 | Magic functions |
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117 | 116 | =============== |
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118 | 117 | |
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119 | 118 | IPython has a set of predefined 'magic functions' that you can call with a |
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120 | 119 | command line style syntax. There are two kinds of magics, line-oriented and |
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121 | 120 | cell-oriented. **Line magics** are prefixed with the ``%`` character and work |
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122 | 121 | much like OS command-line calls: they get as an argument the rest of the line, |
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123 | 122 | where arguments are passed without parentheses or quotes. **Line magics** can |
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124 | 123 | return results and can be used in the right hand side of an assignment. **Cell |
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125 | 124 | magics** are prefixed with a double ``%%``, and they are functions that get as |
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126 | 125 | an argument not only the rest of the line, but also the lines below it in a |
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127 | 126 | separate argument. |
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128 | 127 | |
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129 | 128 | Magics are useful as convenient functions where Python syntax is not the most |
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130 | 129 | natural one, or when one want to embed invalid python syntax in their work flow. |
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131 | 130 | |
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132 | 131 | The following examples show how to call the built-in :magic:`timeit` magic, both |
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133 | 132 | in line and cell mode:: |
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134 | 133 | |
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135 | 134 | In [1]: %timeit range(1000) |
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136 | 135 | 179 ns Β± 2.66 ns per loop (mean Β± std. dev. of 7 runs, 10000000 loops each) |
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137 | 136 | |
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138 | 137 | In [2]: %%timeit x = range(10000) |
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139 | 138 | ...: max(x) |
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140 | 139 | ...: |
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141 | 140 | 264 Β΅s Β± 1 Β΅s per loop (mean Β± std. dev. of 7 runs, 1000 loops each) |
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142 | 141 | |
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143 | 142 | The built-in magics include: |
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144 | 143 | |
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145 | 144 | - Functions that work with code: :magic:`run`, :magic:`edit`, :magic:`save`, |
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146 | 145 | :magic:`macro`, :magic:`recall`, etc. |
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147 | 146 | |
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148 | 147 | - Functions which affect the shell: :magic:`colors`, :magic:`xmode`, |
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149 | 148 | :magic:`automagic`, etc. |
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150 | 149 | |
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151 | 150 | - Other functions such as :magic:`reset`, :magic:`timeit`, |
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152 | 151 | :cellmagic:`writefile`, :magic:`load`, or :magic:`paste`. |
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153 | 152 | |
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154 | 153 | You can always call magics using the ``%`` prefix, and if you're calling a line |
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155 | 154 | magic on a line by itself, as long as the identifier is not defined in your |
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156 | 155 | namespace, you can omit even that:: |
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157 | 156 | |
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158 | 157 | run thescript.py |
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159 | 158 | |
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160 | 159 | You can toggle this behavior by running the :magic:`automagic` magic. Cell |
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161 | 160 | magics must always have the ``%%`` prefix. |
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162 | 161 | |
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163 | 162 | A more detailed explanation of the magic system can be obtained by calling |
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164 | 163 | ``%magic``, and for more details on any magic function, call ``%somemagic?`` to |
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165 | 164 | read its docstring. To see all the available magic functions, call |
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166 | 165 | ``%lsmagic``. |
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167 | 166 | |
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168 | 167 | .. seealso:: |
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169 | 168 | |
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170 | 169 | The :ref:`magic` section of the documentation goes more in depth into how |
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171 | 170 | the magics works and how to define your own, and :doc:`magics` for a list of |
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172 | 171 | built-in magics. |
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173 | 172 | |
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174 | 173 | `Cell magics`_ example notebook |
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175 | 174 | |
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176 | 175 | Running and Editing |
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177 | 176 | ------------------- |
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178 | 177 | |
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179 | 178 | The :magic:`run` magic command allows you to run any python script and load all |
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180 | 179 | of its data directly into the interactive namespace. Since the file is re-read |
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181 | 180 | from disk each time, changes you make to it are reflected immediately (unlike |
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182 | 181 | imported modules, which have to be specifically reloaded). IPython also includes |
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183 | 182 | :ref:`dreload <dreload>`, a recursive reload function. |
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184 | 183 | |
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185 | 184 | ``%run`` has special flags for timing the execution of your scripts (-t), or |
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186 | 185 | for running them under the control of either Python's pdb debugger (-d) or |
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187 | 186 | profiler (-p). |
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188 | 187 | |
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189 | 188 | The :magic:`edit` command gives a reasonable approximation of multi-line editing, |
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190 | 189 | by invoking your favorite editor on the spot. IPython will execute the |
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191 | 190 | code you type in there as if it were typed interactively. Note that for |
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192 | 191 | :magic:`edit` to work, the call to startup your editor has to be a blocking |
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193 | 192 | call. In a GUI environment, your editor likely will have such an option. |
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194 | 193 | |
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195 | 194 | Debugging |
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196 | 195 | --------- |
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197 | 196 | |
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198 | 197 | After an exception occurs, you can call :magic:`debug` to jump into the Python |
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199 | 198 | debugger (pdb) and examine the problem. Alternatively, if you call :magic:`pdb`, |
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200 | 199 | IPython will automatically start the debugger on any uncaught exception. You can |
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201 | 200 | print variables, see code, execute statements and even walk up and down the call |
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202 | 201 | stack to track down the true source of the problem. This can be an efficient way |
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203 | 202 | to develop and debug code, in many cases eliminating the need for print |
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204 | 203 | statements or external debugging tools. |
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205 | 204 | |
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206 | 205 | You can also step through a program from the beginning by calling |
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207 | 206 | ``%run -d theprogram.py``. |
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208 | 207 | |
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209 | 208 | History |
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210 | 209 | ======= |
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211 | 210 | |
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212 | 211 | IPython stores both the commands you enter, and the results it produces. You |
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213 | 212 | can easily go through previous commands with the up- and down-arrow keys, or |
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214 | 213 | access your history in more sophisticated ways. |
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215 | 214 | |
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216 | 215 | Input and output history are kept in variables called ``In`` and ``Out``, keyed |
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217 | 216 | by the prompt numbers, e.g. ``In[4]``. The last three objects in output history |
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218 | 217 | are also kept in variables named ``_``, ``__`` and ``___``. |
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219 | 218 | |
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220 | 219 | You can use the ``%history`` magic function to examine past input and output. |
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221 | 220 | Input history from previous sessions is saved in a database, and IPython can be |
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222 | 221 | configured to save output history. |
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223 | 222 | |
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224 | 223 | Several other magic functions can use your input history, including ``%edit``, |
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225 | 224 | ``%rerun``, ``%recall``, ``%macro``, ``%save`` and ``%pastebin``. You can use a |
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226 | 225 | standard format to refer to lines:: |
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227 | 226 | |
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228 | 227 | %pastebin 3 18-20 ~1/1-5 |
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229 | 228 | |
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230 | 229 | This will take line 3 and lines 18 to 20 from the current session, and lines |
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231 | 230 | 1-5 from the previous session. |
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232 | 231 | |
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233 | 232 | System shell commands |
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234 | 233 | ===================== |
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235 | 234 | |
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236 | 235 | To run any command at the system shell, simply prefix it with ``!``, e.g.:: |
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237 | 236 | |
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238 | 237 | !ping www.bbc.co.uk |
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239 | 238 | |
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240 | 239 | You can capture the output into a Python list, e.g.: ``files = !ls``. To pass |
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241 | 240 | the values of Python variables or expressions to system commands, prefix them |
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242 | 241 | with $: ``!grep -rF $pattern ipython/*`` or wrap in `{braces}`. See :ref:`our |
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243 | 242 | shell section <system_shell_access>` for more details. |
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244 | 243 | |
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245 | 244 | Define your own system aliases |
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246 | 245 | ------------------------------ |
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247 | 246 | |
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248 | 247 | It's convenient to have aliases to the system commands you use most often. This |
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249 | 248 | allows you to work seamlessly from inside IPython with the same commands you are |
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250 | 249 | used to in your system shell. IPython comes with some pre-defined aliases and a |
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251 | 250 | complete system for changing directories, both via a stack (see :magic:`pushd`, |
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252 | 251 | :magic:`popd` and :magic:`dhist`) and via direct :magic:`cd`. The latter keeps a |
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253 | 252 | history of visited directories and allows you to go to any previously visited |
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254 | 253 | one. |
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255 | 254 | |
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256 | 255 | |
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257 | 256 | Configuration |
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258 | 257 | ============= |
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259 | 258 | |
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260 | 259 | Much of IPython can be tweaked through :doc:`configuration </config/intro>`. |
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261 | 260 | To get started, use the command ``ipython profile create`` to produce the |
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262 | 261 | default config files. These will be placed in |
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263 | 262 | :file:`~/.ipython/profile_default`, and contain comments explaining |
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264 | 263 | what the various options do. |
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265 | 264 | |
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266 | 265 | Profiles allow you to use IPython for different tasks, keeping separate config |
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267 | 266 | files and history for each one. More details in :ref:`the profiles section |
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268 | 267 | <profiles>`. |
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269 | 268 | |
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270 | 269 | .. _startup_files: |
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271 | 270 | |
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272 | 271 | Startup Files |
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273 | 272 | ------------- |
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274 | 273 | |
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275 | 274 | If you want some code to be run at the beginning of every IPython session, the |
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276 | 275 | easiest way is to add Python (.py) or IPython (.ipy) scripts to your |
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277 | 276 | :file:`profile_default/startup/` directory. Files here will be executed as soon |
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278 | 277 | as the IPython shell is constructed, before any other code or scripts you have |
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279 | 278 | specified. The files will be run in order of their names, so you can control the |
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280 | 279 | ordering with prefixes, like ``10-myimports.py``. |
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281 | 280 | |
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282 | 281 | .. include:: ../links.txt |
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