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1 1 .. _tutorial:
2 2
3 3 ======================
4 4 Introducing IPython
5 5 ======================
6 6
7 7 You don't need to know anything beyond Python to start using IPython – just type
8 8 commands as you would at the standard Python prompt. But IPython can do much
9 9 more than the standard prompt. Some key features are described here. For more
10 10 information, check the :ref:`tips page <tips>`, or look at examples in the
11 11 `IPython cookbook <https://github.com/ipython/ipython/wiki/Cookbook%3A-Index>`_.
12 12
13 13 If you haven't done that yet see `how to install ipython <install>`_ .
14 14
15 15 If you've never used Python before, you might want to look at `the official
16 16 tutorial <http://docs.python.org/tutorial/>`_ or an alternative, `Dive into
17 17 Python <http://diveintopython.net/toc/index.html>`_.
18 18
19 19 Start IPython by issuing the ``ipython`` command from your shell, you should be
20 20 greeted by the following::
21 21
22 22 Python 3.6.0
23 23 Type 'copyright', 'credits' or 'license' for more information
24 24 IPython 6.0.0.dev -- An enhanced Interactive Python. Type '?' for help.
25 25
26 26 In [1]:
27 27
28 28
29 29 Unlike the Python REPL, you will see that the input prompt is ``In [N]:``
30 30 instead of ``>>>``. The number ``N`` in the prompt will be used later in this
31 31 tutorial but should usually not impact the computation.
32 32
33 33 You should be able to type single line expressions and press enter to evaluate
34 34 them. If an expression is incomplete, IPython will automatically detect this and
35 add a new line when you press ``Enter`` instead of executing right away.
35 add a new line when you press :kbd:`Enter` instead of executing right away.
36 36
37 37 Feel free to explore multi-line text input. Unlike many other REPLs, with
38 38 IPython you can use the up and down arrow keys when editing multi-line
39 39 code blocks.
40 40
41 41 Here is an example of a longer interaction with the IPython REPL,
42 42 which we often refer to as an IPython *session* ::
43 43
44 44 In [1]: print('Hello IPython')
45 45 Hello IPython
46 46
47 47 In [2]: 21 * 2
48 48 Out[2]: 42
49 49
50 50 In [3]: def say_hello(name):
51 51 ...: print('Hello {name}'.format(name=name))
52 52 ...:
53 53
54 54 We won't get into details right now, but you may notice a few differences to
55 55 the standard Python REPL. First, your code should be syntax-highlighted as you
56 56 type. Second, you will see that some results will have an ``Out[N]:`` prompt,
57 57 while some other do not. We'll come to this later.
58 58
59 Depending on the exact command you are typing you might realize that sometime
60 the :key:`Enter` will add a new line, and sometime it will execute the current
59 Depending on the exact command you are typing you might realize that sometimes
60 :kbd:`Enter` will add a new line, and sometimes it will execute the current
61 61 statement. IPython tries to guess what you are doing, so most of the time you
62 62 should not have to care. Though if by any chance IPython does not the right
63 63 thing you can force execution of the current code block by pressing in sequence
64 :key:`Esc` and :key:`Enter`. You can also force the insertion of a new line at
65 the position of the cursor by using `Ctrl-O`.
64 :kbd:`Esc` and :kbd:`Enter`. You can also force the insertion of a new line at
65 the position of the cursor by using :kbd:`Ctrl-o`.
66 66
67 67 The four most helpful commands
68 68 ==============================
69 69
70 70 The four most helpful commands, as well as their brief description, is shown
71 71 to you in a banner, every time you start IPython:
72 72
73 73 ========== =========================================================
74 74 command description
75 75 ========== =========================================================
76 76 ? Introduction and overview of IPython's features.
77 77 %quickref Quick reference.
78 78 help Python's own help system.
79 79 object? Details about 'object', use 'object??' for extra details.
80 80 ========== =========================================================
81 81
82 82 Tab completion
83 83 ==============
84 84
85 85 Tab completion, especially for attributes, is a convenient way to explore the
86 86 structure of any object you're dealing with. Simply type ``object_name.<TAB>``
87 87 to view the object's attributes. Besides Python objects and keywords, tab
88 88 completion also works on file and directory names.
89 89
90 90 Starting with IPython 6.0, if ``jedi`` is installed, IPython will try to pull
91 completions from Jedi as well. This allow to not only inspect currently
91 completions from Jedi as well. This allows to not only inspect currently
92 92 existing objects, but also to infer completion statically without executing
93 code. There is nothing particular to do this to work, simply use tab
94 completion on more complex expression like the following::
93 code. There is nothing particular need to get this to work, simply use tab
94 completion on more complex expressions like the following::
95 95
96 96 >>> data = ['Number of users', 123_456]
97 97 ... data[0].<tab>
98 98
99 99 IPython and Jedi will be able to infer that ``data[0]`` is actually a string
100 100 and should show relevant completions like ``upper()``, ``lower()`` and other
101 string methods. You can use the Tab key to cycle through completions, and while
102 a completion is highlighted, its type will be shown as well.
101 string methods. You can use the :kbd:`Tab` key to cycle through completions,
102 and while a completion is highlighted, its type will be shown as well.
103 103
104 104 Exploring your objects
105 105 ======================
106 106
107 107 Typing ``object_name?`` will print all sorts of details about any object,
108 108 including docstrings, function definition lines (for call arguments) and
109 109 constructor details for classes. To get specific information on an object, you
110 110 can use the magic commands ``%pdoc``, ``%pdef``, ``%psource`` and ``%pfile``
111 111
112 112 .. _magics_explained:
113 113
114 114 Magic functions
115 115 ===============
116 116
117 117 IPython has a set of predefined 'magic functions' that you can call with a
118 118 command line style syntax. There are two kinds of magics, line-oriented and
119 119 cell-oriented. **Line magics** are prefixed with the ``%`` character and work
120 120 much like OS command-line calls: they get as an argument the rest of the line,
121 121 where arguments are passed without parentheses or quotes. **Lines magics** can
122 122 return results and can be used in the right hand side of an assignment. **Cell
123 123 magics** are prefixed with a double ``%%``, and they are functions that get as
124 124 an argument not only the rest of the line, but also the lines below it in a
125 125 separate argument.
126 126
127 127 Magics are useful as convenient functions where Python syntax is not the most
128 128 natural one, or when one want to embed invalid python syntax in their work flow.
129 129
130 The following examples show how to call the builtin :magic:`timeit` magic, both
130 The following examples show how to call the built-in :magic:`timeit` magic, both
131 131 in line and cell mode::
132 132
133 133 In [1]: %timeit range(1000)
134 134 100000 loops, best of 3: 7.76 us per loop
135 135
136 136 In [2]: %%timeit x = range(10000)
137 137 ...: max(x)
138 138 ...:
139 139 1000 loops, best of 3: 223 us per loop
140 140
141 The builtin magics include:
141 The built-in magics include:
142 142
143 143 - Functions that work with code: :magic:`run`, :magic:`edit`, :magic:`save`,
144 144 :magic:`macro`, :magic:`recall`, etc.
145 145
146 146 - Functions which affect the shell: :magic:`colors`, :magic:`xmode`,
147 147 :magic:`autoindent`, :magic:`automagic`, etc.
148 148
149 149 - Other functions such as :magic:`reset`, :magic:`timeit`,
150 150 :cellmagic:`writefile`, :magic:`load`, or :magic:`paste`.
151 151
152 152 You can always call magics using the ``%`` prefix, and if you're calling a line
153 153 magic on a line by itself, as long as the identifier is not defined in your
154 154 namespace, you can omit even that::
155 155
156 156 run thescript.py
157 157
158 158 You can toggle this behavior by running the :magic:`automagic` magic. Cell
159 159 magics must always have the ``%%`` prefix.
160 160
161 161 A more detailed explanation of the magic system can be obtained by calling
162 162 ``%magic``, and for more details on any magic function, call ``%somemagic?`` to
163 163 read its docstring. To see all the available magic functions, call
164 164 ``%lsmagic``.
165 165
166 166 .. seealso::
167 167
168 168 The :ref:`magic` section of the documentation goes more in depth into how
169 169 the magics works and how to define your own, and :doc:`magics` for a list of
170 170 built-in magics.
171 171
172 172 `Cell magics`_ example notebook
173 173
174 174 Running and Editing
175 175 -------------------
176 176
177 177 The :magic:`run` magic command allows you to run any python script and load all
178 178 of its data directly into the interactive namespace. Since the file is re-read
179 179 from disk each time, changes you make to it are reflected immediately (unlike
180 180 imported modules, which have to be specifically reloaded). IPython also includes
181 181 :ref:`dreload <dreload>`, a recursive reload function.
182 182
183 183 ``%run`` has special flags for timing the execution of your scripts (-t), or
184 184 for running them under the control of either Python's pdb debugger (-d) or
185 185 profiler (-p).
186 186
187 The :magic:`edit` command gives a reasonable approximation of multiline editing,
187 The :magic:`edit` command gives a reasonable approximation of multi-line editing,
188 188 by invoking your favorite editor on the spot. IPython will execute the
189 189 code you type in there as if it were typed interactively. Note that for
190 190 :magic:`edit` to work, the call to startup your editor has to be a blocking
191 191 call. In a GUI environment, your editor likely will have such an option.
192 192
193 193 Debugging
194 194 ---------
195 195
196 196 After an exception occurs, you can call :magic:`debug` to jump into the Python
197 197 debugger (pdb) and examine the problem. Alternatively, if you call :magic:`pdb`,
198 198 IPython will automatically start the debugger on any uncaught exception. You can
199 199 print variables, see code, execute statements and even walk up and down the call
200 200 stack to track down the true source of the problem. This can be an efficient way
201 201 to develop and debug code, in many cases eliminating the need for print
202 202 statements or external debugging tools.
203 203
204 204 You can also step through a program from the beginning by calling
205 205 ``%run -d theprogram.py``.
206 206
207 207 History
208 208 =======
209 209
210 210 IPython stores both the commands you enter, and the results it produces. You
211 211 can easily go through previous commands with the up- and down-arrow keys, or
212 212 access your history in more sophisticated ways.
213 213
214 214 Input and output history are kept in variables called ``In`` and ``Out``, keyed
215 215 by the prompt numbers, e.g. ``In[4]``. The last three objects in output history
216 216 are also kept in variables named ``_``, ``__`` and ``___``.
217 217
218 218 You can use the ``%history`` magic function to examine past input and output.
219 219 Input history from previous sessions is saved in a database, and IPython can be
220 220 configured to save output history.
221 221
222 222 Several other magic functions can use your input history, including ``%edit``,
223 223 ``%rerun``, ``%recall``, ``%macro``, ``%save`` and ``%pastebin``. You can use a
224 224 standard format to refer to lines::
225 225
226 226 %pastebin 3 18-20 ~1/1-5
227 227
228 228 This will take line 3 and lines 18 to 20 from the current session, and lines
229 229 1-5 from the previous session.
230 230
231 231 System shell commands
232 232 =====================
233 233
234 234 To run any command at the system shell, simply prefix it with ``!``, e.g.::
235 235
236 236 !ping www.bbc.co.uk
237 237
238 238 You can capture the output into a Python list, e.g.: ``files = !ls``. To pass
239 239 the values of Python variables or expressions to system commands, prefix them
240 240 with $: ``!grep -rF $pattern ipython/*``. See :ref:`our shell section
241 241 <system_shell_access>` for more details.
242 242
243 243 Define your own system aliases
244 244 ------------------------------
245 245
246 246 It's convenient to have aliases to the system commands you use most often. This
247 247 allows you to work seamlessly from inside IPython with the same commands you are
248 248 used to in your system shell. IPython comes with some pre-defined aliases and a
249 249 complete system for changing directories, both via a stack (see :magic:`pushd`,
250 250 :magic:`popd` and :magic:`dhist`) and via direct :magic:`cd`. The latter keeps a
251 251 history of visited directories and allows you to go to any previously visited
252 252 one.
253 253
254 254
255 255 Configuration
256 256 =============
257 257
258 258 Much of IPython can be tweaked through :doc:`configuration </config/intro>`.
259 259 To get started, use the command ``ipython profile create`` to produce the
260 260 default config files. These will be placed in
261 261 :file:`~/.ipython/profile_default`, and contain comments explaining
262 262 what the various options do.
263 263
264 264 Profiles allow you to use IPython for different tasks, keeping separate config
265 265 files and history for each one. More details in :ref:`the profiles section
266 266 <profiles>`.
267 267
268 268 .. _startup_files:
269 269
270 270 Startup Files
271 271 -------------
272 272
273 273 If you want some code to be run at the beginning of every IPython session, the
274 274 easiest way is to add Python (.py) or IPython (.ipy) scripts to your
275 275 :file:`profile_default/startup/` directory. Files here will be executed as soon
276 276 as the IPython shell is constructed, before any other code or scripts you have
277 277 specified. The files will be run in order of their names, so you can control the
278 278 ordering with prefixes, like ``10-myimports.py``.
279 279
280 280 .. include:: ../links.txt
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