CoCalc Public FilesTest.ipynb
Authors: Tomoko Kuroki, Jorge Tower
Views : 154
Description: Testing python
In [1]:
type(3)

int
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type(3.2)

float
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int(6/3)

2
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"This is a string"

'This is a string'
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"or type str"

'or type str'
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type("ofcourse")

str
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"aeiou".replace("a", "t")

'teiou'
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"hulo".replace("o", "u")

'hulu'
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"    sadness     ".strip()

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b = [300 * 3,2,3 + 2]

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a = [1,4,5]

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b[0]

900
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a[2]

5
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[1,3,6][1]

3
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b[1:2]

[2]
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b[0:2]

[900, 2]
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b[0:3]

[900, 2, 5]
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a[0:2]

[1, 4]
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c = 2
c = c + 4
c

6
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a = 1
b = 2
c = a + b
c

3
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I_m_a_variable = 2

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I_m_a_variable

2
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1variable = 2

 File "<ipython-input-28-672ad970f03b>", line 1 1variable = 2 ^ SyntaxError: invalid syntax 
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a = 1
b = 5
c = 3
a + b - c

3
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a = 4
b = 2
c = 1
a + b - c

5
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def example():
a = 4
b = 2
c = 1
return a + b - c

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type(example)

function
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example()

5
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def example2():
a=5
b=6
c=9
return a-b+c

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type(example2)

function
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example2()

8
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def example(a, b, c):
return a + b - c

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example(1, 5, 2)

4
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example(2, 4, 3)

3
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def example(a,b,c):
return a-b+c


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example(1,4,9)

6
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example(3, 2, 1 + 1)

3
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fileDescriptor = open("example.txt", "wt")
fileDescriptor.write("This is a text example")
fileDescriptor.close()

In [50]:
help(open)

Help on built-in function open in module io: open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None) Open file and return a stream. Raise IOError upon failure. file is either a text or byte string giving the name (and the path if the file isn't in the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.) mode is an optional string that specifies the mode in which the file is opened. It defaults to 'r' which means open for reading in text mode. Other common values are 'w' for writing (truncating the file if it already exists), 'x' for creating and writing to a new file, and 'a' for appending (which on some Unix systems, means that all writes append to the end of the file regardless of the current seek position). In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are: ========= =============================================================== Character Meaning --------- --------------------------------------------------------------- 'r' open for reading (default) 'w' open for writing, truncating the file first 'x' create a new file and open it for writing 'a' open for writing, appending to the end of the file if it exists 'b' binary mode 't' text mode (default) '+' open a disk file for updating (reading and writing) 'U' universal newline mode (deprecated) ========= =============================================================== The default mode is 'rt' (open for reading text). For binary random access, the mode 'w+b' opens and truncates the file to 0 bytes, while 'r+b' opens the file without truncation. The 'x' mode implies 'w' and raises an FileExistsError if the file already exists. Python distinguishes between files opened in binary and text modes, even when the underlying operating system doesn't. Files opened in binary mode (appending 'b' to the mode argument) return contents as bytes objects without any decoding. In text mode (the default, or when 't' is appended to the mode argument), the contents of the file are returned as strings, the bytes having been first decoded using a platform-dependent encoding or using the specified encoding if given. 'U' mode is deprecated and will raise an exception in future versions of Python. It has no effect in Python 3. Use newline to control universal newlines mode. buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows: * Binary files are buffered in fixed-size chunks; the size of the buffer is chosen using a heuristic trying to determine the underlying device's "block size" and falling back on io.DEFAULT_BUFFER_SIZE. On many systems, the buffer will typically be 4096 or 8192 bytes long. * "Interactive" text files (files for which isatty() returns True) use line buffering. Other text files use the policy described above for binary files. encoding is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent, but any encoding supported by Python can be passed. See the codecs module for the list of supported encodings. errors is an optional string that specifies how encoding errors are to be handled---this argument should not be used in binary mode. Pass 'strict' to raise a ValueError exception if there is an encoding error (the default of None has the same effect), or pass 'ignore' to ignore errors. (Note that ignoring encoding errors can lead to data loss.) See the documentation for codecs.register or run 'help(codecs.Codec)' for a list of the permitted encoding error strings. newline controls how universal newlines works (it only applies to text mode). It can be None, '', '\n', '\r', and '\r\n'. It works as follows: * On input, if newline is None, universal newlines mode is enabled. Lines in the input can end in '\n', '\r', or '\r\n', and these are translated into '\n' before being returned to the caller. If it is '', universal newline mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated. * On output, if newline is None, any '\n' characters written are translated to the system default line separator, os.linesep. If newline is '' or '\n', no translation takes place. If newline is any of the other legal values, any '\n' characters written are translated to the given string. If closefd is False, the underlying file descriptor will be kept open when the file is closed. This does not work when a file name is given and must be True in that case. A custom opener can be used by passing a callable as *opener*. The underlying file descriptor for the file object is then obtained by calling *opener* with (*file*, *flags*). *opener* must return an open file descriptor (passing os.open as *opener* results in functionality similar to passing None). open() returns a file object whose type depends on the mode, and through which the standard file operations such as reading and writing are performed. When open() is used to open a file in a text mode ('w', 'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open a file in a binary mode, the returned class varies: in read binary mode, it returns a BufferedReader; in write binary and append binary modes, it returns a BufferedWriter, and in read/write mode, it returns a BufferedRandom. It is also possible to use a string or bytearray as a file for both reading and writing. For strings StringIO can be used like a file opened in a text mode, and for bytes a BytesIO can be used like a file opened in a binary mode.
In [51]:
help(max)

Help on built-in function max in module builtins: max(...) max(iterable, *[, default=obj, key=func]) -> value max(arg1, arg2, *args, *[, key=func]) -> value With a single iterable argument, return its biggest item. The default keyword-only argument specifies an object to return if the provided iterable is empty. With two or more arguments, return the largest argument.
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help(fileDescriptor)

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a = 2
if a == 2:
print("It is 2")

It is 2
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a = True
type(a)

bool
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a == 2

False
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a = 3
a == 3

True
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3 > 2

True
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a = 9
a = a + 1
if a > 9:
print("It's big!")
if a < 9:
print("Not enough big")

It's big!

# The if conditional

An if is a keyword used to define a block of code that can be executed or not if the statement after the if is a true boolean

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if True:
print("Obviously, it's true")

Obviously, it's true

so we can use operators to get facts about our variables like the equalty operator

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a = 2
if a == 2:
print("It's 2")

It's 2
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if a == 3:
print("It's 3")


Sometimes, we would like check the trueness of various statements. for that we can use the operator and

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if a > 1 and a < 5:
print("It's between 1 and 5")

It's between 1 and 5

or maybe if one of the statements is true

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if a == 2 or a == 3:
print("It's or 2 or 3")

It's or 2 or 3

That's the basis of the if construction but there is 2 adjacent keywords that can be used for the next purpouses:

if we want run code if a if block code isn't run, then we can use else

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if a == 5:
print("It's five")
else:
print("It's not five")

It's not five

note that as we're using two different blocks of code, the else token has the left space remmoved as represents the beginning of another block of code

sometimes, we need execute only one block of a serie of conditional blocks, that why we have else if, in python called elif

In [72]:
a = 5
if a == 2:
print("It's 2")
elif a > 1 and a < 10:
print("It's between 1 and 10")
elif a > 900:
print("It's over nine-haundred")
elif a < 50:
print("It's less than 50")
else:
print("I don't know what number is")

It's between 1 and 10

Note that it could have run the block, less than 50 but didn't because, it found first the elif block of a > 1 and a < 10, then executed it and due the other blocks being elif, ignored the rest

# While construction

Programs keep being useless if they can't repeat a block of code as many times we want because, programs exist for do the work that people doesn't want to do

a while is a keyword that defines a block executed as many times as the expression after while is True

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a = 1
while a < 10:
print("It's " + str(a))
a = a + 1

It's 1 It's 2 It's 3 It's 4 It's 5 It's 6 It's 7 It's 8 It's 9

As happened with if we can apply all features of a statement into that sentence after while

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a = 100
while a > 10 and a / 2 != 20:
print("It's " + str(a))
a = a - 10

It's 100 It's 90 It's 80 It's 70 It's 60 It's 50

Probably you guessed that if == is equalty, then != is the inequalty or not equal. In this example, we find what number divided by 2 results into 20 and the answer is 50 as you can see. Notice that normally facts in a while are the opposite of what normally we will say "a / 2 == 20" because we need that result of that expression being True for make while to run the block code again

Loops have 2 keywords that can be used inside their block, we will show it implementing a search on a list

In [80]:
a = [1, 20, 30, 50, 900]
i = 0
while a[i] < 100:
i = i + 1
a[i]

900

ok, we have the item that we searched in the list but what if we want stop it if we find 30?

In [83]:
a = [1, 20, 30, 50, 900]
i = 0
while a[i] < 100 and a[i] != 30:
i = i + 1
a[i]

30

for that we didn't have to introduce any new keyword Kappa

But sometimes, conditions can be really long or even uncalculable until we do some operations. Let's find a number that contains a 3

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def contains3(value):
value = str(value)
i = 0
contains = False
while i < len(value):
if value[i] == "3":
contains = True
i = i + 1
return contains

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a = [1, 20, 23, 30, 50, 900]
i = 0
while a[i] < 100 and not contains3(a[i]):
i = i + 1
a[i]

23

We see new things in these examples like the operator not that reverses the result of a boolean statement (What is True becomes False and opposite). The other thing that we see is that a string is indexable, you can access to a letter of it using [] and the position.

oh, wait that problem didn't use any new keyword... but how the fuck can we do the same without grouping a piece of code in a function?

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a = [1, 20, 23, 30, 50, 900]
i = -1
contains3 = False
while i < 0 or (a[i] < 100 and not contains3):
i = i + 1
value = str(a[i])
z = 0
contains3 = False
while z < len(value):
if value[z] == "3":
contains3 = True
z = z + 1
a[i]>

23

Yep, we're looking what seems a nested loop while. In these ocassion, exit the loop when we want using the condition of the first while can be tricky. As you can see, we had to put the increment of i at the beginning because we don't want increment when we detect the number with 3 and due that, we had to start with i being -1

What about i < 0? Well, you can guess that if we ask the member -1 of a list will complain, so we need to protect that incorrect access making loop before that sentence with the a[i] is evaluated. That's why i < 0 is there.

There is two quirks about the evaluation of conditionals. First is that languages will try anything to save run code. If the first condition in that sentence is True, then doesn't matter what says the other part of or and will not evaluate it (Making not evaluating that a[-1]). The second thing is that we group sentences in () to dictate the order of evaluation, first we want evaluate i < 0 and after that, what is inside ()

### break to the rescue

Last example was not an easy example of how make nested loop that need exit in some point that isn't evaluable in the conditional. Fortunately, we have the keyword break which simply breaks the loop

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a = [1, 20, 23, 30, 50, 900]
i = 0
while a[i] < 100:
z = 0
value = str(a[i])
contains3 = False
while z < len(value):
if value[z] == "3":
contains3 = True
z = z + 1
if contains3:
break
i = i + 1
a[i]

23

That's way better :p

The other keyword is continue and what it does is end the code block of the loop and make another iteration (Basically, it's like it jumped to the end of the loop code)

## Exercise

Find all numbers up to 1000 that the division between the number and 10, contains 0 and write it on a file

For that, you should have enough with all the code posted in this notebook and you only need to know that the string "\n" is used to indicate when there is a new line

In [ ]:
fd  = open("numbers.txt", "wt")
i = 0
while i < 1000:
contains0 = False

if contains0:
fd.write(str(i) + "\n")
i = i + 1
fd.close()

In [ ]: