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1 | 1 | ================= |
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2 | 2 | Python vs IPython |
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3 | 3 | ================= |
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4 | 4 | |
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5 | 5 | This document is meant to highlight the main differences between the Python |
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6 | 6 | language and what are the specific construct you can do only in IPython. |
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7 | 7 | |
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8 | 8 | Unless expressed otherwise all of the construct you will see here will raise a |
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9 | 9 | ``SyntaxError`` if run in a pure Python shell, or if executing in a Python |
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10 | 10 | script. |
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11 | 11 | |
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12 | 12 | Each of these features are describe more in details in further part of the documentation. |
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13 | 13 | |
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14 | 14 | |
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15 | 15 | Quick overview: |
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16 | 16 | =============== |
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17 | 17 | |
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18 | 18 | |
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19 | 19 | All the following construct are valid IPython syntax: |
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20 | 20 | |
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21 | 21 | .. code-block:: ipython |
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22 | 22 | |
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23 | 23 | In [1]: ? |
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24 | 24 | |
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25 | 25 | .. code-block:: ipython |
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26 | 26 | |
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27 | 27 | In [1]: ?object |
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28 | 28 | |
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29 | 29 | |
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30 | 30 | .. code-block:: ipython |
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31 | 31 | |
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32 | 32 | In [1]: object? |
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33 | 33 | |
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34 | 34 | .. code-block:: ipython |
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35 | 35 | |
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36 | 36 | In [1]: *pattern*? |
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37 | 37 | |
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38 | 38 | .. code-block:: ipython |
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39 | 39 | |
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40 | 40 | In [1]: %shell like --syntax |
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41 | 41 | |
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42 | 42 | .. code-block:: ipython |
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43 | 43 | |
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44 | 44 | In [1]: !ls |
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45 | 45 | |
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46 | 46 | .. code-block:: ipython |
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47 | 47 | |
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48 |
In [1]: my_files =! |
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48 | In [1]: my_files = !ls ~/ | |
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49 | 49 | In [1]: for i,file in enumerate(my_file): |
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50 | 50 | ...: raw = !echo $file |
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51 | 51 | ...: !echo {files[0].upper()} $raw |
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52 | 52 | |
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53 | 53 | |
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54 | 54 | .. code-block:: ipython |
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55 | 55 | |
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56 | 56 | In [1]: %%perl magic --function |
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57 | 57 | ...: @months = ("July", "August", "September"); |
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58 | 58 | ...: print $months[0]; |
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59 | 59 | |
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60 | 60 | |
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61 | 61 | Each of these construct is compile by IPython into valid python code and will |
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62 | 62 | do most of the time what you expect it will do. Let see each of these example |
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63 | 63 | in more detail. |
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64 | 64 | |
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65 | 65 | |
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66 | 66 | Accessing help |
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67 | 67 | ============== |
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68 | 68 | |
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69 | 69 | As IPython is mostly an interactive shell, the question mark is a simple |
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70 | 70 | shortcut to get help. A question mark alone will bring up the IPython help: |
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71 | 71 | |
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72 | 72 | .. code-block:: ipython |
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73 | 73 | |
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74 | 74 | In [1]: ? |
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75 | 75 | |
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76 | 76 | IPython -- An enhanced Interactive Python |
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77 | 77 | ========================================= |
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78 | 78 | |
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79 | 79 | IPython offers a combination of convenient shell features, special commands |
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80 | 80 | and a history mechanism for both input (command history) and output (results |
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81 | 81 | caching, similar to Mathematica). It is intended to be a fully compatible |
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82 | 82 | replacement for the standard Python interpreter, while offering vastly |
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83 | 83 | improved functionality and flexibility. |
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84 | 84 | |
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85 | 85 | At your system command line, type 'ipython -h' to see the command line |
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86 | 86 | options available. This document only describes interactive features. |
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87 | 87 | |
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88 | 88 | MAIN FEATURES |
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89 | 89 | ------------- |
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90 | 90 | ... |
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91 | 91 | |
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92 | 92 | A single question mark before, or after an object available in current |
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93 | 93 | namespace will show help relative to this object: |
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94 | 94 | |
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95 | 95 | .. code-block:: ipython |
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96 | 96 | |
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97 | 97 | In [6]: object? |
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98 | 98 | Docstring: The most base type |
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99 | 99 | Type: type |
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100 | 100 | |
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101 | 101 | |
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102 | 102 | A double question mark will try to pull out more information about the object, |
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103 | 103 | and if possible display the python source code of this object. |
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104 | 104 | |
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105 | 105 | .. code-block:: ipython |
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106 | 106 | |
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107 | 107 | In[1]: import collections |
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108 | 108 | In[2]: collection.Counter?? |
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109 | 109 | |
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110 | 110 | Init signature: collections.Counter(*args, **kwds) |
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111 | 111 | Source: |
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112 | 112 | class Counter(dict): |
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113 | 113 | '''Dict subclass for counting hashable items. Sometimes called a bag |
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114 | 114 | or multiset. Elements are stored as dictionary keys and their counts |
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115 | 115 | are stored as dictionary values. |
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116 | 116 | |
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117 | 117 | >>> c = Counter('abcdeabcdabcaba') # count elements from a string |
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118 | 118 | |
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119 | 119 | >>> c.most_common(3) # three most common elements |
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120 | 120 | [('a', 5), ('b', 4), ('c', 3)] |
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121 | 121 | >>> sorted(c) # list all unique elements |
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122 | 122 | ['a', 'b', 'c', 'd', 'e'] |
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123 | 123 | >>> ''.join(sorted(c.elements())) # list elements with repetitions |
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124 | 124 | 'aaaaabbbbcccdde' |
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125 | 125 | ... |
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126 | 126 | |
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127 | 127 | |
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128 | 128 | |
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129 | 129 | If you are looking for an object, the use of wildcards ``*`` in conjunction |
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130 | 130 | with question mark will allow you to search current namespace for object with |
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131 | 131 | matching names: |
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132 | 132 | |
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133 | 133 | .. code-block:: ipython |
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134 | 134 | |
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135 | 135 | In [24]: *int*? |
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136 | 136 | FloatingPointError |
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137 | 137 | int |
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138 | 138 | |
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139 | 139 | |
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140 | 140 | |
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141 | 141 | Shell Assignment |
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142 | 142 | ================ |
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143 | 143 | |
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144 | 144 | |
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145 | 145 | When doing interactive computing it is common to need to access the underlying shell. |
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146 | 146 | This is doable through the use of the exclamation mark ``!`` (or bang). |
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147 | 147 | |
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148 | 148 | This allow to execute simple command when present in beginning of line: |
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149 | 149 | |
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150 | 150 | .. code-block:: ipython |
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151 | 151 | |
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152 | 152 | In[1]: !pwd |
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153 | 153 | /User/home/ |
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154 | 154 | |
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155 | 155 | Change directory: |
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156 | 156 | |
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157 | 157 | .. code-block:: ipython |
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158 | 158 | |
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159 | 159 | In[1]: !cd /var/etc |
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160 | 160 | |
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161 | 161 | Or edit file: |
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162 | 162 | |
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163 | 163 | .. code-block:: ipython |
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164 | 164 | |
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165 | 165 | In[1]: !mvim myfile.txt |
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166 | 166 | |
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167 | 167 | |
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168 | 168 | The line after the bang can call any program installed in the underlying |
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169 | 169 | shell, and support variable expansion in the form of ``$variable`` or ``{variable}``. |
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170 | 170 | The later form of expansion supports arbitrary python expression: |
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171 | 171 | |
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172 | 172 | .. code-block:: ipython |
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173 | 173 | |
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174 | 174 | In[1]: file = 'myfile.txt' |
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175 | 175 | |
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176 | 176 | In[2]: !mv $file {file.upper()} |
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177 | 177 | |
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178 | 178 | |
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179 | 179 | The bang can also be present in the right hand side of an assignment, just |
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180 | 180 | after the equal sign, or separated from it by a white space. In which case the |
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181 | 181 | standard output of the command after the bang ``!`` will be split out into lines |
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182 | 182 | in a list-like object and assign to the left hand side. |
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183 | 183 | |
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184 | 184 | This allow you for example to put the list of files of the current working directory in a variable: |
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185 | 185 | |
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186 | 186 | .. code-block:: ipython |
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187 | 187 | |
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188 |
In[1]: my_files =! |
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188 | In[1]: my_files = !ls | |
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189 | 189 | |
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190 | 190 | |
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191 | 191 | You can combine the different possibilities in for loops, condition, functions...: |
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192 | 192 | |
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193 | 193 | .. code-block:: ipython |
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194 | 194 | |
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195 |
my_files =! |
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195 | my_files = !ls ~/ | |
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196 | 196 | b = "backup file" |
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197 | 197 | for i,file in enumerate(my_file): |
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198 | 198 | raw = !echo $backup $file |
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199 | 199 | !cp $file {file.split('.')[0]+'.bak'} |
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200 | 200 | |
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201 | 201 | |
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202 | 202 | Magics |
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203 | 203 | ------ |
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204 | 204 | |
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205 | 205 | Magics function are often present in the form of shell-like syntax, but are |
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206 | 206 | under the hood python function. The syntax and assignment possibility are |
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207 | 207 | similar to the one with the bang (``!``) syntax, but with more flexibility and |
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208 | 208 | power. Magic function start with a percent sign (``%``) or double percent (``%%``). |
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209 | 209 | |
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210 | 210 | A magic call with a sign percent will act only one line: |
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211 | 211 | |
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212 | 212 | .. code-block:: ipython |
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213 | 213 | |
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214 | 214 | In[1]: %xmode |
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215 | 215 | Exception reporting mode: Verbose |
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216 | 216 | |
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217 | 217 | And support assignment: |
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218 | 218 | |
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219 | 219 | .. code-block:: ipython |
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220 | 220 | |
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221 | 221 | In [1]: results = %timeit -r1 -n1 -o list(range(1000)) |
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222 | 222 | 1 loops, best of 1: 21.1 µs per loop |
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223 | 223 | |
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224 | 224 | In [2]: results |
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225 | 225 | Out[2]: <TimeitResult : 1 loops, best of 1: 21.1 µs per loop> |
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226 | 226 | |
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227 | 227 | Magic with two percent sign can spread over multiple lines, but do not support assignment: |
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228 | 228 | |
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229 | 229 | .. code-block:: ipython |
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230 | 230 | |
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231 | 231 | In[1]: %%bash |
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232 | 232 | ... : echo "My shell is:" $SHELL |
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233 | 233 | ... : echo "My disk usage is:" |
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234 | 234 | ... : df -h |
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235 | 235 | My shell is: /usr/local/bin/bash |
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236 | 236 | My disk usage is: |
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237 | 237 | Filesystem Size Used Avail Capacity iused ifree %iused Mounted on |
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238 | 238 | /dev/disk1 233Gi 216Gi 16Gi 94% 56788108 4190706 93% / |
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239 | 239 | devfs 190Ki 190Ki 0Bi 100% 656 0 100% /dev |
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240 | 240 | map -hosts 0Bi 0Bi 0Bi 100% 0 0 100% /net |
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241 | 241 | map auto_home 0Bi 0Bi 0Bi 100% 0 0 100% /hom |
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242 | 242 | |
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243 | 243 | |
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244 | 244 | Combining it all |
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245 | 245 | ---------------- |
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246 | 246 | |
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247 | 247 | :: |
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248 | 248 | |
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249 | 249 | find a snippet that combine all that into one thing! |
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