05c-strings.ipynb

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    "# Programming with Python (lab classes)\n",
    "#### Vedran Šego, [vsego.org](http://vsego.org/)\n",
    "\n",
    "## Content:\n",
    "\n",
    "1. Strings\n",
    "\n",
    "2. Generators"
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    "**Problem 1.** Write a program that loads a list of strings and prints them sorted, ignoring their character case (so called **case insensitive** comparison).\n",
    "\n",
    "For example:\n",
    "* case sensitive: `\"John\" < \"alien\"`, because all capital letters come before all lower case letters;\n",
    "* case insensitive: `\"John\" > \"alien\"`, because the case is ignored, so it is the same as `\"john\" > \"alien\"`).\n",
    "\n",
    "**Note:** The original strings in the list should not be altered in any way!\n",
    "\n",
    "**Hint:** Using [`str.tolower()`](https://docs.python.org/3/library/stdtypes.html#str.lower) in combination with the `key` argument of `sort` and a `lambda`-function might help you."
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    "**Problem 2.** Write a function `del_double(s, char_del, char_double)` that returns a new string obtained from `s` by removing all the occurrences of the character `char_del` and doubling all the occurrences of the character `char_double`. If `char_del` is not given, nothing should be removed. Similarly, if `char_double` is not given, nothing should be doubled.\n",
    "\n",
    "For example,\n",
    "* `del_double(\"abcdbacabcd\", \"b\", \"d\")` should return `\"acddacacdd\"`,\n",
    "* `del_double(\"abcdbacabcd\", \"b\")` should return `\"acdacacd\"`,\n",
    "* `del_double(\"abcdbacabcd\", s_double=\"d\")` should return `\"abcddbacabcdd\"`,\n",
    "* `del_double(s)` should return a copy of `s`.\n",
    "\n",
    "If `char_del == char_double`, then no doubling will take place because the deletions will remove all the occurences of `char_del` (which are the same as the occurences of `char_double`).\n",
    "\n",
    "**Note:** In `del_double`, you may assume that `len(char_del) == len(char_double) == 1`, but make sure that this is correct when loading the data.\n",
    "\n",
    "**Hint:** Write an auxiliary function that will take three characters `c`, `c_del`, and `c_double`, and return\n",
    "* an empty string if `c == c_del`,\n",
    "* double `c` if `c == c_double`,\n",
    "* `c` otherwise.\n",
    "\n",
    "Then use this function in a list comprehension that traverses through the string `s`."
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    "**Problem 3.** Write a function `time_diff(t1, t2)` that returns the absolute time difference between the times `t1` and `t2`. Each of them is given as a string formated either as `hh:mm:ss` or as `mm:ss`. The returned difference should have the same format (`hh` part should be omitted if it equals zero), with each part taking up at least two digits.\n",
    "\n",
    "For example,\n",
    "* `time_diff(\"17:19:23\", \"13:11:7\")` should return `\"04:08:16\"`;\n",
    "* `time_diff(\"13:11:7\", \"17:19:23\")` should also return `\"04:08:16\"` (because the function returns the absolute time difference);\n",
    "* `time_diff(\"17:19:23\", \"11:7\")` should return `\"17:08:16\"`;\n",
    "* `time_diff(\"17:19:23\", \"17:11:7\")` should return `\"08:16\"`.\n",
    "\n",
    "**Hint:** Write two auxiliary functions, `str2time` and `time2str`, that will convert the string of the described format to the number of seconds since the beginning of the day (`3600*hh+60*mm+ss`) and vice versa."
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    "**Problem 4.** Write a function `remove(s, chrs, case_sensitive)` that returns a string obtained from `s` by removing all the characters present in `chrs`. The parameter `case_sensitive` is Boolean; if it is `True`, the matching is case sensitive; otherwise it is insensitive. If the function is invoked with only two arguments, the match should be case sensitive.\n",
    "\n",
    "For example, `remove(s, \"0123456789\")` would return the copy of `s` without any digits it may have had. So, `remove(\"a12b0 c\", \"0123\")` would return `\"ab c\"`. Similarly, `remove(s, \"A\")` would return a copy of `s` without upper case letters \"`A`\" (but all lower case letters \"`a`\" would remain intact). However, `remove(s, \"A\", True)` would return a copy of `s` without any letters \"`A`\", lower case or upper case.\n",
    "\n",
    "Preferably, use a generator expression to create this new string."
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    "**Program 5.** Write a function `load_a_list_of_ints_as_a_string()` that loads a list of integers with a singe call to `input`. Assume that the it will be given in the form `\"x1,x2,...,xn\"`. For example, `\"17,-19,23\"` (without spaces or any characters other than a single comma between each two neighbour integers).\n",
    "\n",
    "Write a program that uses this function to load a list of integers, and print it sorted in a descended order."
   ]
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